题目内容
在3.5英寸的软盘上有一个带滑块的小方孔，其作用是
查看答案
搜索结果不匹配？点我反馈
更多问题
Most growing plants contain much more water than all other materials combined. C. R. Darnes has suggested that it is as proper to term the plant a water structure as to call a house composed mainly of bricks a brick building. Certain it is that all essential processes of plant growth and development occur in water. The mineral elements from the soil that are usable by the plant must be dissolved in the soil solution before they can be taken into the root. They are carried to all parts of the growing plant and are built into essential plant materials while in a dissolved state.' The carbon dioxide from the air may enter the leaf as a gas but is dissolved in water in the leaf before it is combined with a part of the water to form. simple sugars—the base material from which the plant body is mainly built. Actively growing plant parts are generally 75 to 90 percent water. Structural parts of plants, such as woody stems no longer actively growing, may have much less water than growing tissues.
The actual amount of water in the plant at any one time, however, is only a very small part of what passes through it during its development. The processes of photosynthesis, by which carbon dioxide and water are combined—in the presence of chlorophyll (叶绿素) and with energy derived from light to form. sugars, require that carbon dioxide from the air enter the plant. This occurs mainly in the leaves. The leaf surface is not solid but contains great numbers of minute (细小的) openings, through which the carbon dioxide enters. The same structure that permits the one gas to enter the leaf, however, permits another gas—water vapor to be lost from it. Since carbon dioxide is present in the air only in trace quantities (3 to 4 parts in 10, 000 parts of air) and water vapor is near saturation in the air spaces within the leaf (at 80 F , saturated air would contain about 186 parts of water vapor in 10,000 parts of air), the total amount of water vapor lost is many times the carbon dioxide intake. Actually, because of wind and other factors, the loss of water in proportion to carbon dioxide intake may be even greater than the relative concentrations of the two gases. Also, not all of the carbon dioxide that enters the leaf is synthesized into carbohydrates(碳水化合物).
A growing plant needs water for all of the following except ______.
听力原文： Now and again I have had horrible dreams, but not enough of them to make me lose my delight in dreams. To begin with, I like the idea of dreaming, of going to bed and lying still and then, by some magic, wandering into another world. Most people or at least most Western Europeans do not seem to accept dreaming as part of their lives. They appear to see it as an irritating little habit, like sneezing or yawning. I have never understood this. My dream life does not seem as important as my waking life, if only because there is far less of it, but to me it is important.
Then again, the dream life has its own advantages. The dead are there, smiling and talking. The past is there, and perhaps, the future is there too, winking at us. This dream life is often overshadowed by huge mysterious anxieties, with luggage that cannot be packed and trains that refuse to be caught; and both persons and scenes there are not as dependable and solid as they are in waking life, so that Brown and Smith become one person while Robinson breaks into two; and there are moments of terror in the dream world that are worse than anything we have known under the sun. Yet this other life has its interests, its fun and its satisfaction.
(33)
A．The girl.B．The bottle.C．The pirate ship.D．The dream.
A．Why people have dreams at night.B．Why the speaker enjoys dreaming.C．Why dreams are n
微信支付 
支付宝支付