Since +時間點，具體時間自從、、、、以來，從、、、以后” 用來說明動作起始時間

　　I have been in Beijing since 2010.

　　For + 時間段，用來說明動作延續時間長度，因此句中的謂語動詞，也應該是延續性動詞。

　　I have been in Beijing for one year.

　　for +一段時間

　　since +句子

　　since +一段時間+ ago

　　since +時間點

　　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