for和since的用法有什么不同

问题描述:

for和since的用法有什么不同
都用于现在完成时,但具体怎么分

很简单.
since+时间点/ 句子,for+时间段
1 I have been here for about 10 years.
2 I have been here since 10 years ago
3 I have been here since I was 10 years old.
4 I have been here since 2001