—I won't get good grades_______ I study hard.

                                 —That's ______ everyone is trying his best to prepare for the exam.

对海洋污染最为严重的是（　　）

李良在学习中做了个“错题本”，专门记录做错的题，用来思考问题的规律、特点等，他的这一做法是获得了（    ）

You must ____ (finish) your homework and hand it in as soon as the class is over.