题目

Hundreds of years ago, life was harder than it is today. People didn’t have modern machines. There was no modern medicine, either. Life today has brought new problems. One of the biggest is pollution. Water pollution has made our rivers and lakes dirty. It kills our fish and pollutes our drinking water. Noise pollution makes us talk louder and become angry more easily. Air pollution is the most serious kind of pollution to all living things in the world. Cars, planes and factories all pollute our air every day. Sometimes the polluted air is so thick that it is like a quilt over a ci计算：（1）sin30°-2cos60°（2）cos230°+sin230°-tan45°．