◆他能通過考試。

誤：He can be able to pass the exam.

正：He can pass the exam. / He is able to pass the exam.

析：be able to 不能與 can 用在同一個謂語中。

◆這工作可按時完成。

誤：The work is able to be finished in time.

正：The work is capable of being finished in time.

正：The work can be finished in time.

析：按規范語法：be able to之后一般不接動詞的被動式，盡管在 現代英語中已有人打破此規則，但初學者仍以不用為宜。

◆他在公共汽車后面追，并追上了。

誤：He ran after the bus, and could catch it.

正：He ran after the bus, and was able to catch it.

析：表示過去特定情況下的能力，可用 was (were) able to 而不 能用 could，不過這種差異在否定句中便不存在了。如：He ran after the bus but wasn’t able to [couldn’t] catch it.