英语中的连词that在许多情况下可以省略，包括在宾语从句、表语从句、同位语从句和某些状语从句中。但在某些动词后面，如admit, declare, explain等，以及在某些被动语态中，不能省略that。总的来说，that的使用非常灵活，但在大部分情况下都可以省略。
1. 宾语从句
在宾语从句中，常常可以省略that。例如：
- She said (that) she was tired.
- He thinks (that) he is the best candidate.
- I hope (that) you have a good day.
2. 表语从句
在表语从句中，that也常常可以省略。例如：
- His idea is (that) we should invest more in technology.
- The fact is (that) we are running out of time.
- The problem seems (that) it cannot be solved.
3. 同位语从句
同位语从句指的是解释、说明或重述名词的从句，that在这种情况下也可以省略。例如：
- The news (that) he won the prize was exciting.
- My belief (that) hard work pays off has been proven true.
- The idea (that) we should work together is a good one.
4. 状语从句
在某些状语从句中，也可以省略that。例如：
- After he finished his work, he went home.
- When I saw her, I knew she was upset.
- If you need help, just ask me.
需要注意的是，有些情况下不能省略that，例如在某些动词后面，如admit, declare, explain等，以及在某些被动语态中。因此，在使用that时，需要根据具体情况来决定是否省略。
