已知 $\frac{1}{2}{x}^m{y}^3$ 与﹣2xyⁿ是同类项，则m-n=____．

 在我国古代的改革中，其中发生在春秋战国时期和南北朝时期的两次最为有名。请问：
（1）这是两次什么改革？
（2）这两次改革的目的各是什么？在当时分别起到了什么作用？

补全对话, 每空一句。

Doctor: Good morning! ____

Tom: Tom.

Doctor: ____

Tom: I'm not feeling well. I have a toothache and I can't eat anything.

Doctor: When did it start?

Tom: ____

Doctor: Let me examine you. Open your mouth and say "Ah", please.

Tom: Ah……Is it serious?

Doctor: ____ Just stop eating candies and take the medicine. You will feel better soon.

Tom: How often should I take the medicine?

Doctor: ____

Tom: Thank you.