Since +时间点，具体时间自从、、、、以来，从、、、以后” 用来说明动作起始时间
I have been in Beijing since 2010.
For + 时间段，用来说明动作延续时间长度，因此句中的谓语动词，也应该是延续性动词。
I have been in Beijing for one year.
for +一段时间
since +句子
since +一段时间+ ago
since +时间点
例如 he has been dead for three years
he has been dead since three years ago
He has studied English since 2003
He has studied English since he was ten years old
