英语中的 AS 和 SINCE 都是表示时间的词汇，但是它们在用法上有一些区别。
AS 的用法
AS 可以表示时间的点或时刻，常用于以下情况：
- 表示某个具体的时间点，例如：
- I'll meet you at the coffee shop as soon as I finish work.
- The train leaves as soon as the passengers are on board.
- 表示某个事件的同时发生的时间，例如：
- As I was walking down the street, I saw an old friend.
- She smiled as she read the letter from her boyfriend.
- 表示身份、职业等，例如：
- As a teacher, I think it's important to encourage students to ask questions.
- He spoke as a representative of the company.
SINCE 的用法
SINCE 通常表示从某个时间点开始一直持续到现在，常用于以下情况：
- 表示某个具体时间点之后的时间，例如：
- I haven't seen him since last week.
- She's been studying English since she was a child.
- 表示某个事件的开始，例如：
- We've been waiting for the bus since 10 o'clock.
- I've been feeling tired since I got up this morning.
- 表示原因或理由，例如：
- He's been absent from work since he got sick.
- I haven't been able to sleep since I drank coffee in the evening.
总之，AS 是表示时间的点或时刻，而 SINCE 是表示从某个时间点开始一直持续到现在。希望读者能够掌握它们的用法，提高英语表达能力。
