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Unit 4 by Mind Map: Unit 4

1. Past perfect tense

1.1. Use the past perfect tense (had+past participle ) to indicate an action that happed before another action in the past

1.1.1. When we arrived at the airport, our flight had already left.

2. Can't , could , couldn't ,must , May, or might

2.1. Past

2.1.1. It couldn't be...., It might have been...

2.2. Present

2.2.1. It can't be... , It might be ...