each of them knows what the others are doing.这里的knows为什么加s
she is intersting to talk to 这里的talk 后面把to去掉为什么不对，
to hear him talk in that manner，you would think he is a foreigner。talk in 这里的in去掉行吗 to hear 改成 hearing行吗 为什么吗
和 he was amusing to be with。with是不是省略了什么 把with去掉对吗为什么