since

ad. 后来
conj. 既然,因为
prep. 自从

Since you can't answer the question, perhaps we'd better ask someone else.

既然你无法回答这个问题，我们最好再问问别人。

We've been friends ever since we met at school.

自从我们在学校认识之后，我们就一直是好朋友。