each of them knows what the others are doing.这里的knows为什么加sshe 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

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