8. as if / though引起的從句

當as if / though引起的從句所表達的內容完全與實際情況相反或者純粹是一種假設時，通常要用虛擬語氣。如果從句表示與現在的事實相反，謂語動詞用一般過去時;如果從句表示與過去的事實相反，謂語動詞用過去完成時;如果從句表示與將來的事實相反，謂語動詞用would （might， could） + 動詞原形;

They talked as if they had been friends for years.

I remember the whole thing as if it happened yesterday.

It looks as if it might rain.

Note： 如果as if / though引起的從句所表達的內容被看作是事實或者有可能是真實的，則要用陳述語氣。

It seems as if it is going to rain.

The meat tastes as if it has already gone bad.

9. lest， for fear that和 in case引起的從句

當lest， for fear that和 in case表示“以免，以防，生怕，惟恐”等時，在它們引起的從句中，謂語動詞常用should + 動詞原形。

He ran away lest he should be seen.

He’s working hard for fear that he should fall behind.

He left early in case he should miss the last train.