since的四種用法
1) since +過去一個時間點 (如具體的年、月、日期、鐘點、1980, last month, half past six)。
I have been here since 1989.
2) since +一段時間+ ago
I have been here since five months ago.
3) since +從句
Great changes have taken place since you left.
Considerable time has elapsed since we have been here.
4) It is +一段時間+ since從句
It is two years since I became a postgraduate student.
PETS－2語法講解(29)
'一般現(xiàn)在時的用法 1) 經(jīng)常性或習(xí)慣性的動作，常與表示頻腮度的時間狀語連用。時間狀語：every…, sometimes, at…, on SundayI leave home for school at 7 every morning. 2) 客觀真理，客觀存在，科學(xué)事實...'
PETS－2語法講解(28)
'感官動詞 + doing/to do 感官動詞 see, watch, observe, notice, look at, hear, listen to, smell, taste, feel + do 表示動作的完整性，真實性；+doing 表示動作的連續(xù)性，進行性I saw him work in the gard...'
PETS－2語法講解(20)
regret doing/to do regret to do 對要做的事遺憾。 (未做) regret doing 對做過的事遺憾、后悔。 (已做) I regret to have to do this, but I have no choice. 我很遺憾必須這樣去做，...
PETS－2語法講解(18)
'用現(xiàn)在進行時表示將來 意為："意圖"、"打算"、"安排"、常用于人。常用詞為 come, go, start, arrive, leave, stay等。I'm leaving tomorrow.Are you staying here till next week?EN010...'
