1.enough
2.We did not go to school last Friday.
= There were (no classes) for us last Friday.
He (finished doing) his homework two days ago.
3.答案：didn't you（楼主可能是把2打错字了）
一般过去时,前句为实义动词went,所以用didn't.
4.答案：3.Listen,hear
listen to后面必须有宾语才可以,如Listen to me.如果其后没有宾语,只需要用listen即可；
hear是及物动词,表示听到的结果,而listen (to...)强调动作.