Only one pump operates overnight. Choose the standard sentence.
The pump which operate overnight is in the basement.
The pump which operating overnight is in the basement.
The pump which operates overnight is in the basement.✓Correct answer
The pump which are operating overnight is in the basement.
Explanation
Which refers to the singular pump, so operates agrees with that antecedent in the present tense. Operate and are operating require a plural subject, while the bare participle does not provide a finite relative verb.