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如果一组变量值中有一项为零，则不能计算（）。
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Earth Angels
(1) Joying Brescia was 8 years old when she noticed that cigarette butts (烟头) were littering her hometown beach in Isle of Palms, South Carolina. When she learned that it takes five years for the remains of a cigarette to disintegrate, she decided to take action. Joying launched a "No Butts on the Beach" campaign. She raised money and awareness about the need to keep the beaches clean. With the help of others, Joying also bought or received donations of gallon-size plastic ice-cream buckets. The buckets were filled with sand and placed at all public-access areas of the beach. The buckets allowed people to dispose of their cigarettes before hitting .the beach. Two years later. Joying says the buckets are full and the beach is nearly free of cigarette debris (残片).
(2) People who live in or visit Steamboat Springs, Colorado have Carter Dunham to thank for a new state wildlife refuge that preserves 20 acres of marshland and many species of wildlife.
Carter and other students wrote a management plan for the area around the Yampa River. The plan was part of a class project when Carter was a freshman at Steamboat Springs High School. Working with the Colorado Division of Wildlife, Carter and his classmates mapped the area and species of animals living there. They also made decisions about, among other things, where fences and parking areas should be built.
(3) Barbara Brown and her friends collect oil. It started as a project for their 4H Club after one of the girls noticed her father using motor oil to kill weeds on their farm in Victoria, Texas. They did some research and discovered that oil can contaminate ground water, a real danger in rural areas, where people live off the water on their land. The girls researched ways to recycle oil and worked with a local oil-recycling company on the issue. Now, the "Don&39;t Be Crude" program runs oil collection sites--tanks that hold up to 460 gallons--where people in the community can dispose of their oil.
(4) Five years ago, 11-year-old Ryan Hreljac was a little boy with a big dream: for all the people in Africa to have clean drinking water. His dream began in the first grade when he learned that people were dying because they didn&39;t have clean water, and that as little as $70 could build a well. "We really take water for granted," says Ryan, of Kemptville, Ontario, in Canada. "In other countries, you have to plan for it." Ryan eamed the first $70 by doing extra chores (零工) , but with the help of others, he has since raised hundreds of thousands of dollars.
(5) His efforts led to the start of the Ryan&39;s Well Foundation, which raises money for clean water and health-related services for people in African countries and developing countries.
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Earth Angels
（1） Joying Brescia was 8 years old when she noticed that cigarette butts （烟头） were littering her hometown beach in Isle of Palms， South Carolina. When she learned that it takes five years for the remains of a cigarette to disintegrate， she decided to take action. Joying launched a "No Butts on the Beach" campaign. She raised money and awareness about the need to keep the beaches clean. With the help of others， Joying also bought or received donations of gallon-size plastic ice-cream buckets. The buckets were filled with sand and placed at all public-access areas of the beach. The buckets allowed people to dispose of their cigarettes before hitting the beach. Two years later. Joying says the buckets are full and the beach is nearly free of cigarette debris （残片） .
（2） People who live in or visit Steamboat Springs， Colorado have Carter Dunham to thank for a new state wildlife refuge that preserves 20 acres of marshland and many species of wildlife.
Carter and other students wrote a management plan for the area around the Yampa River. The plan was part of a class project when Carter was a freshman at Steamboat Springs High School. Working with the Colorado Division of Wildlife， Carter and his classmates mapped the area and species of animals living there. They also made decisions about， among other things， where fences and parking areas should be built.
（3） Barbara Brown and her friends collect oil. It started as a project for their 4H Club after one of the girls noticed her father using motor oil to kill weeds on their farm in Victoria， Texas. They did some research and discovered that oil can contaminate ground water， a real danger in rural areas， where people live off the water on their land. The girls researched ways to recycle oil and worked with a local oil-recycling company on the issue. Now， the "Don"t Be Crude" program runs oil collection sites——tanks that hold up to 460 gallons- where people in the community can dispose of their oil.
（4） Five years ago， 11-year-old Ryan Hreljac was a little boy with a big dream: for all the people in Africa to have clean drinking water. His dream began in the first grade when he learned that people were dying because they didn"t have clean water， and that as little as $70 could build a well. "We really take water for granted，" says Ryan， of Kemptville，Ontario， in Canada. "In other countries， you have to plan for it." Ryan earned the first $70 by doing extra chores （零工） ， but with the help of others， he has since raised hundreds of thousands of dollars.
（5） His efforts led to the start of the Ryan"s Well Foundation， which raises money for clean water and health-related services for people in African countries and developing countries.
Paragraph 1__________. 查看材料
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Spacing in Animals Flight Distance
Any observant person has noticed that a wild animal will allow a man or other potential enemy to approach only up to a given distance before it flees. "Flight distance" is the terms used for this interspecies spacing. As a general rule, there is a positive relationship between the size of an animal and its flight distance- the larger the animal, the greater the distance it must keep between itself and the enemy. An antelope will flee when the enemy is as much as five hundred yards away. The wall lizard&39;s flight distance, on the other hand is about six feet. Flight is the basic means of survival for mobile creatures.
Critical Distance Critical distance apparently is present wherever and whenever there is a flight reaction.
"Critical distance" includes the narrow zone separating flight distance from attack distance. A lion in a zoo will flee from an approaching man until it meets a barrier that it cannot overcome. If the man continues the approach, he soon penetrates the lion&39;s critical distance, at which point the cornered lion reverses direction and begins slowly to stalk the man.
Social Distance Social animals need to stay in touch with each other. Loss of contact with the group can be fatal for a variety of reasons including exposure to enemies. Social distance is not simply the distance at which an animal will lose contact with his group -- that is, the distance at which it can no longer see, hear, or smell the group- it is rather a psychological distance, one at which the animal apparently begins to feel anxious when he exceeds its limits. We can think of it as a hidden band that contains the group.
Social distance varies from species to species. It is quite short--apparently only a few yards--among some animals, and quite long among others.
Social distance is not always rigidly fixed but is determined in part by the situation. When the young of apes and humans are mobile but not yet under control of the mother&39;s voice, social distance may be the length of her reach. This is readily observed among the baboons in a zoo.
When the baby approaches a certain point, the mother reaches out to seize the end of its tail and pull it back to her. When added control is needed because of danger, social distance shrinks. To show this in man, one has only to watch a family with a number of small children holding hands as they cross a busy street.
Which of the following is the most appropriate definition of Flight Distance？ 查看材料
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