关键句型一：表示过去与现在的对比的句型（以本题“学生减负后，过去与现在的对比”为例）
1. i had to work on weekends doing endless homework and attending classes in the past. however, things have changed a lot now. i have more free time.
2. i used to have to work even on weekends doing endless homework and attending classes. now i have more free time.
3. in the past, i had to work on weekends doing endless homework and attending classes. but now i have more free time.
4. it's quite different now. i used to have to work even on weekends doing endless homework and attending classes, but now i have more free time.
5. it's not like it used to be at all. now i have more free time.
6. i have more free time than before.