Since +時間點(diǎn)，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(xù)時間長度，因此句中的謂語動詞，也應(yīng)該是延續(xù)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(diǎn)

　　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