题目内容
听力原文： In this lesson, I want to talk about the history of The White House. At first, most Americans didn't think there was anything particularly special about the White House. Few had ever seen it or had any idea what it looked like, and even the families who lived there found it completely inadequate. When it was built, the White House was the largest house in the country and it remained so until after the Civil War. But it served so many different purposes that little of it was available for the First Family to actually live in. The first floor, or "State Floor" was made up entirely of public rooms; and the president's offices, which where staffed by as many as 30 employees, took half of the second floor up. The First Family had to get by with the eight or fewer second-floor rooms that were left. By Lincoln's time, the situation was intolerable. The White House was open to visitors; office seekers, and the merely curious had no difficulty making their way upstairs from the official rooms on the first floor. Lincoln was so uncomfortable with the situation that he had a private corridor constructed. He also received a $ 20, 000 appropriation to improve the furnishings of the White House. The new furnishings did not last for more than a few years. When Lincoln was assassinated in 1865, the White House fell into disarray. No one really supervised the White House during' the first five weeks.
(30)
查看答案
搜索结果不匹配？点我反馈
更多问题
听力原文：W: How did your interview go？
M: I couldn't feel better about it.
Q: What does the man feel about the interview？
(14)
听力原文：M: Didn't you tell Tom about the meeting？
W: Whatever I say to him goes in one ear and out the other.
Q: What does the woman mean？
(13)
The biggest advantage provided by NGVs is that they' help reduce car accidents to a great
Natural-gas Vehicles
Kermit the Frog once said, "It's not that easy bein' green." Although he wasn't referring to cars, his observation seems particularly appropriate for the auto industry today: Designing, developing and marketing "green" cars has not been an easy task, which is why gasoline-powered vehicles still rule the road and fossil fuels still account for almost 75 percent of the world' s energy consumption. As gasoline prices soar and concern over harmful emission mounts, how ever, cars that run on alternate fuel sources will become increasingly important. A natural-gas vehicle, or NGV, is the perfect example of such a car -- it's fuel-efficient, environmentally friendly and offers a relatively low cost of ownership.
Natural Gas Basics
The word "gas" is a confusing term because it is used to describe many different substances that are similar but not exactly the same. For example, tile "gas" you put in your car is gasoline, one component of crude oil, or petroleum. Petroleum is a dark, sticky liquid mixture of compounds formed underground by the decay of ancient marine animals.
Natural gas also comes from the decay of ancient organisms, but it naturally takes a gaseous form. instead of a liquid form. Natural gas commonly occurs in association with crude oil. It is derived from both land plants and aquatic organic matter and forms above or below oil deposits. It is often dissolved in crude oil at the high pressures existing in a reservoir. There are also reservoirs of natural gas, known as non-associated gas, that contain only gas and no oil.
Natural gas consists primarily of methane and other hydrocarbon gases. Hydrocarbons are organic compounds composed only of the elements carbon and hydrogen. The hydrocarbons in natural gas are called saturated hydrocarbons because they contain hydrogen and carbon bound together by single bonds.
Like gasoline, natural gas is combustible, which means it can be used in a combustion engine like gasoline. But cars that could burn natural gas didn't appear on the scene until the 1930s.
From Field to Ford
We extract natural gas trapped in underground reservoirs by drilling wells into the earth. A modern well, equipped with diamond-studded drill bits, can drill to depths approaching 25,000 feet.
Throughout the 19th century, the use of natural gas remained localized because there was no way to transport large quantities of gas over long distances. In 1890, the invention of a leak proof pipeline coupling made it possible to transport gas miles from the source. Improvements in pipeline technology continued over the next two decades until long-distance gas transmission became practical. From 1927 to 1931, laborers constructed more than 10 major natural gas transmission systems in the United States, making natural gas a viable energy source for many applications. The oil shortages of the late 1960s and early 1970s brought renewed interest in natural gas as a fuel source, especially for automobiles.
Today, owners of natural-gas vehicles can fill up their cars at one of 1,300 fueling stations located in the United States. Honda also offers a personal natural gas pump to people who purchase its natural-gas-powered Civic. The pump uses a home's existing natural gas lines and can be installed for $ 500 to $1500.
Natural-gas Vehicle Design
Natural-gas Vehicles use the same basic principles as gasoline-powered vehicles. In other words, the fuel(natural gas in this case)is mixed with air in the cylinder of a four-stroke engine and then ignited by a spark plug to move a piston up and down. Although there are some differences between natural gas and gasoline in terms of flammability and ignition temperatures, NGVs themselves operate on the same fundamental concepts as gasoline-powered vehicles.
Still, some modifications are required to make an NGV
微信支付 
支付宝支付