On the one hand, cars are very convenient. People can drive their cars to go anywhere at anytime,which is impossible if they take buses because buses have their fixed traveling routes and fixed time of departure and arrival. Besides ,in terms of speed and comfort,cars are incomparable for short trips. Finally,in case of emergency,you can get in your car immediately and drive to your destination without waiting for buses or taxies,which can save your time and sometimes even your life. On the other hand, cars also have their own disadvantages, of which pollution should deserve our consideration. As it is known, the exhaust gases emitted by cars can seriously contaminate the air and even cause people to die if inhale too much. Moreover ,with the number of cars increasing rapidly, the problem of traffic jams is becoming more and more serious. They slow down the speed at which people arrive at their destination. Finally, cars also bring us troubles. For example,we frequently see people anxiously driving their cars looking in vain for a parking space.