Question

Fill in the blank with the most appropriate word.
When the teacher fell off his chair, the students _____.

• A. weren't able to stop laughter
• B. could not stop but laughing
• C. couldn't help laughing
• D. could not avoid to laugh

Answer 1

Answer: (C)

couldn't help laughing

Option C is the correct answer. It correctly uses the modal with the correct form if the verb, the -ing formation, indicating the continual nature of the activity. This form of the verb is compatible with the "help" in the sentence. Options A and D are incorrect for incorporating the incorrect form of the verb. They should also include the -ing form, except the "to" in option D. Option B is also wrong for it also has the incorrect form of the verb. The correct form to go with but is laugh.