In common with many countries, Britain has serious environmental problems. In 1952, more than 4,000 people died in London because of the smog. The government (26) new laws to stop smog from coal fires and factories and the (27) improved a lot. Today, London is much cleaner (28) there is a new problem: smog from cars. In December 1991, there was very (29) wind in London and pollution (30) a lot, which led to 160 deaths in just four days. (31) of the problem is the new "out of town" shopping centers. In the past, people often (32) to shops near their home or went by bus. Today, many people drive to the new shopping centers. (33) , the small shops have (34) and more people have to go a long way to (35) their shopping. Critics say that Britain needs better and cheaper public (36) . Many people are trying to (37) the use of cars in Britain. Some cities now have special bicycle (38) and many people ride to work. Some people also (39) to work together in one car to reduce the pollution and the (40) . Sometimes people take "direct (41) ." In 1995, for example, many people wanted to (42) a new road near Newbury. They built houses (43) trees and lived there for many months. It (44) a long time to force the people out of the trees (45) work on the road could continue.

A. since
B. until
C. though
D. but