请把下面几个句子翻译成英语

Question

中文译成英文：1.英语是一门必修课
2.谁为此事负责？
3.有些人看起来很快乐，有些人看起来很伤心。
4.你们千万不要在大街上玩
5.自那时以来，中国和外界的经济交流大量增加。

Answer 1

1. English is a required course work.
2. Who's responsible for this matter?
3. Some people seem very happy; some seem very sad.
4. Make sure that you do not play in the streets. 或 俗一些就 Don't you guys play in the streets.
5. Since then, the economic exchange between China and the outside world has greatly increased.

Answer 2

1. English is a major/core module.
2. Who is on duty? / Who is responsible for this one?
3. Some people seem very happy, while some other look a little sad.
4. You must not play on the street.
5. Since then, the economic communication between China and other countries/parts has increased rapidly.

Answer 3

1.Who is English required course the 2. is responsible for this matter? 3. some people look like are very joyful, some people look like are very sad. 4. do not play 5. on the avenue since at that time, Chinese and the outside economical exchange increases massively