From the options, choose the word(s) that best fill(s) the gap.
It was a funny episode, I _____.
Answer Details
The best option to fill the blank is "couldn't help laughing".
This is because "help" is a verb that can be followed by a gerund (the -ing form of a verb) but not by an infinitive (the to form of a verb). Therefore, option A "can't help to laugh" and option D "couldn't help to laugh" are both grammatically incorrect.
Between options B "couldn't help laugh" and C "couldn't help laughing", option C is the correct one because the verb "laugh" should be in the -ing form since it functions as a noun in this sentence.
So, the correct sentence is "It was a funny episode, I couldn't help laughing." which means that the person laughed involuntarily because of the humorous situation.