1. He stopped reading a book to watch TV.

2. He stopped walking to watch the accident.

3. He stopped working to take a rest.

4. He stopped watching TV to take a nap.

5. He stopped driving his car to sleep in the car for some time.
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Are the sentences all grammatical?

All are fine, yes. =)

Yes, all of the sentences you provided are grammatically correct. They each follow the pattern of using the verb "stopped" followed by an action that was interrupted or abandoned in order to do something else. "Stopped" is used here to indicate the action of ceasing or pausing the initial activity. The sentences all convey different scenarios where someone interrupts one activity to focus on another.