or接一段時間的省略問題
一、當for引導的時間短語用來修飾具有靜態意義的動詞是常常可以省略。如：
They lived in China (for) seven years.
The meeting lasted (for) two hours.
They will be in Chicago (for) a year.
二、當for與all開頭的名詞短語連用時，必須省略for.
She’s been lying in bed all day.
三、當for短語修飾動態動詞時或者用于否定句是，則借此for不能省略。
I’m going away for a few days.
I haven’t seen him for three weeks.
四、當for用在句子開頭時，一般也不能省略。請比較：
a. He lived abroad (for) six years.
For six years, he lived abroad.
b. He waited anxiously at hospital (for) some time.
For some time, he waited anxiously at hospital.