题目

There is not enough oil in the world now. As time goes by ,it becomes less and less ,so what are we going to do when it runs out? Perhaps we will go back to use horses ,carriages and bicycles .In the Second World War ,some people didn＇t use gas made from petroleum （石油）in their cars .They made gas from wood and plants instead . The cars didn＇t go fast ,but they ran ,so this was better than nothing. However, in the future, we can＇t cut down all our trees to make gas; we need our trees for other things, too.Besides different types of gas, we can also use electricity(电)to run our c6a-9a．