couldとhave P.P.

Review could(~ということもあり得る/ないことはない)
Have P.P.(過去)、理由

A: The worst could happen.
B: Really?
A: That’s why I’ve made a plan for that.

The worst might happen
I made plan for that

1. The event might be delayed.
A big hurricane hit the area last week.

2. My bonus might increase.
I got much better assessment last time.

3. He might be living there.
I visited the apartment last week.

4. My plan might change.
I made an extra plan.

5. She might be sleeping still.
She finished up watching all of the series of the movie.

6. He might have trouble on the job.
I sent an e-mail to make sure.

In your own words

・計画が変更される可能性がある
・その原因は彼にあるかもしれない
・もう誰かそこに住んでいる可能性もある
・彼女が嘘をついている可能性もある
・状況が好転する可能性もある