被動語態和情態動詞結合
(1) 被動語態也可以和情態動詞結合
can/could + be + 動詞過去分詞
may/might
must/have to
should/ought to
had better/would rather
used to/would
特殊：need + doing / to be + 動詞過去分詞
注意：need doing 等價於 need to be done。都表示被動語態，不過need doing常用。
被動語態和情態動詞結合表示：什么應該被怎么樣，必須被怎么樣，加上情態。
1. The food could be taken away. 食物可以被帶走
2. The food might be taken away. 食物可以被帶走
3. The food must be taken away. 食物必須被帶走
4. The food should be taken away. 食物應該被帶走
5. The food needs taking away. 食物需要被帶走。這里的need情態動詞作實意動詞,有人稱時態的變化，needs根據前面不可數名詞變單三形式。need+doing表被動
6. The food had better be taken away. 食物最好被帶走。
7. Books used to be returned in two days. 書過去常常在兩天內被還回去。
上面的除了第5個句子，其他都是情態動詞+動詞的被動語態構成be+done形式。
練習
1. The room may (可能) be cleaned.
2. The door must (必須) be locked.
3. The house should (應該) be furnished.
4. The tree had better (最好) be watered now.