Pollutants coming from automobile operation have begun to cause many environmental problems. It has been calculated, for example, that 70% of the carbon monoxide(一氧化碳), 45% of the nitrogen oxides(氮氧化合物), and 34% of the hydrocarbon (碳氢化合物) pollution in the United States can be traced directly to automobile exhausts (废气). In addition, rubber, motor oil and other materials accumulate on roadways and are washed into streams, with effects nearly as serious as those of untreated waste water.
In an effort to improve the situation, the U.S. government has made regulations on the use of the constituents (成分) of automobile exhaust gas that are known to cause air pollution. These constituents fall roughly into three types: hydrocarbons that pass through the engine unburned; carbon monoxide, also a product of incomplete burning; and nitrogen oxides which are formed when nitrogen and oxygen are in contact at high temperatures. Besides their own poisonous character, hydrocarbons and nitrogen oxides react in the presence of sunlight to form harmful smog. Carbon monoxide and hydrocarbons are rather easily controlled by the use of higher burning temperatures in engines. Unfortunately, the conditions that produce minimum emission of hydrocarbons tend to raise emission of nitrogen oxides. In a way this difficulty is solved by adding recycled exhaust gas to the fuel mixture, thus avoiding the oversupply of oxygen that favors formation of nitrogen oxides.
California, which has the most strict air-pollution laws in the United States, requires further special compounding of gas to control emissions, and several states have ordered that alcohol be mixed with gas, as this will reduce emissions of the carbon monoxide by 35 per cent and the hydrocarbons by 15 per cent.
The author uses figures in Paragraph 1 ________.

A．to reflect the rapid growth of automobile use

B．to highlight the importance of environment protection

C．to show the consequence of automobile exhausts

D．to criticize the low quality of cars

How are nitrogen oxides formed according to the text?

A．Nitrogen and oxygen are put together in great heat.

B．Carbon monoxide and oxygen are mixed together.

C．Hydrocarbons pass through the engine.

D．Nitrogen is burned incompletely.

Which of the following is NOT true according to the text?

A．Carbon monoxide can be controlled in the engine.

B．Smog will form when hydrocarbons meet nitrogen oxides in the sunlight.

C．Hydrocarbons have no poisonous character themselves.

D．The conditions that decease emission of hydrocarbons will increase emission of nitrogen oxides.

According to the text, alcohol is added to gas in order to ______.

A．increase awareness of environment protection

B．control air pollution

C．increase the fuel efficiency

D．replace gas gradually