4 . Directions: Complete the following passage by using the words in the box. Each word can only be used once. Note that there is one word more than you need.
A. constituents B. ultimately C. exhausts D. economical AB. conventional
AC. electricity AD. approximately BC. contributes BD. extent CD. substances
ABC. generates |
Driving an electric car 1 to the protection of environment, or so the marketing departments of their makers would have you believe. Yet a report which analyzes car emissions presents a rather different picture. A battery-powered car recharged with 2 generated by coal-fired power stations, it found, is likely to be more harmful. It could cause more than three times as many deaths from pollution as a 3 petrol-driven vehicle.
The study was carried out by the University of Minnesota. The researchers estimated how levels of fine particulate matter (细颗粒物) and ground-level ozone — two important 4 of air pollution — would change when a car is powered by different ways.
It was no surprise that electric cars whose batteries were recharged with power from wind, solar or hydro-electric sources came out to be virtually free from harmful 5 . They were estimated to cause 231 deaths over the course of a year, compared with 878 for petrol cars. Electric cars recharged with power from natural gas-fired stations were also a lot less harmful than petrol-driven ones, with 439 deaths. But if those same electric cars were recharged 6 by coal, they would be responsible for over 3,000 deaths.
Biofuels also caused more health problems than petrol. But diesel, which often 7 concern about pollution, is slightly cleaner than petrol. This is because the study assumes for all cars that emission-control technologies will be more widely used, especially particulate filters which have a remarkable effect on cleaning diesel 8 . Diesel cars are also more 9 of fuel than petrol-driven ones.
Overall, the study shows that electric cars are cleaner than those traditional vehicles only if the power used to charge then is also clean. That is hardly a surprise, but the 10 of the difference is. How green electric cars really are, then, will depend mainly on where they are driven. In France, which obtains more than half of its power from nuclear station, electric cars look like a good bet. In China and some other developing countries, where a large amount of electricity is produced from coal, they may not be so environment- friendly as they are marketed.
