1.You should buy a good bike if you buy for all.
2.The teacher was angry at us for having disobeyed his orders.
3.A businessman is a man who works on business.
麻烦请教一下原因，谢谢了
參考答案:1. You should buy a good bike if you buy one.
你要买单车就要买个好的.
2. The teacher was angry at us for disobeying his orders.
be angy at sb for doing sth
没有必要强调完成时态
3.A businessman is a man who does business.
生意人就是做生意的嘛.
