Understanding the Idiom 'Couldn't Help'

The question requires you to complete the sentence with the grammatically correct and idiomatically appropriate phrase. The phrase in question is related to the idiom "cannot help" or its past tense form, "couldn't help." This idiom is used to express an uncontrollable action, feeling, or behavior.

The standard structure for this idiom is:

• Cannot help / Couldn't help + Gerund (the -ing form of a verb)

This means that if you "couldn't help laughing," it implies that you were unable to prevent yourself from laughing, usually because something was very funny or compelling.

Analyzing the Options for Sentence Completion

Let's evaluate each given option to determine which one correctly fits the sentence "The movie was funny and I _________."

• Option 1: could help laughing

  This option is incorrect because it reverses the intended meaning of the idiom. "Could help laughing" would mean that the person was able to prevent themselves from laughing, which contradicts the context that the movie was funny and likely elicited an uncontrollable reaction.

• Option 2: couldn’t help laughed

  This option is grammatically incorrect. The idiom "couldn't help" must always be followed by a gerund (the -ing form of the verb). "Laughed" is the simple past tense form of the verb, not a gerund.

• Option 3: couldn’t help laughing

  This option is correct. It perfectly follows the grammatical rule of the idiom: "couldn't help" is followed by the gerund "laughing." This phrase accurately conveys that the person was unable to control their laughter because the movie was very funny.

• Option 4: could helped laughed

  This option is grammatically incorrect. Firstly, the auxiliary verb "could" should be followed by a base form verb (e.g., "help"), not a past participle "helped." Secondly, as discussed, the idiom requires a gerund after "help," not the past tense "laughed."

Completing the Sentence Correctly

Based on the analysis of the idiom's structure and the grammatical correctness of each option, "couldn’t help laughing" is the only choice that fits the sentence properly. It clearly indicates that the movie was so funny that the person found it impossible to stop laughing.

The complete and correct sentence is:
"The movie was funny and I couldn’t help laughing."