In the question below, a part of the sentence is underlined. Below are given alternatives to the underlined part which may improve the sentence. Choose the correct alternative. In case no improvement is needed, choose 'No improvement'. Our usual informant was clamming up when he realized there was a mole in the department. Correct Answer Clammed up The phrasal verb "clam up" means "to suddenly stop, refuse to speak, refrain from disclosing information typically due to a particular reason." Since the rest of the sentence is in simple past,('when he realized'), this verb has to be in simple past tense too. "Was clamming up" is past continuous - So the underlines part is incorrect. "have been clammed up" is present perfect. Option 2 is incorrect. 'Informant' is singular and it will agree with a singular verb - Option 3 "were clammed up" is incorrect as 'were' is used with a plural subject. Correct Sentence: Our usual informant clammed up when he realized there was a mole in the department. It means that the usual informant suddenly shut his mouth on realising there was someone within the department itself (a mole) who was leaking information and defrauding the department. Hence the correct answer is option 1.