During the storm, the glass in three of the windows ___________.

The correct answer is 'Were broken.' In this sentence, the subject 'glass in three of the windows' is plural, so the correct verb form should also be plural, which is 'were broken.' The verb 'broken' in the original sentence is in the past participle form, which is used correctly in the corrected answer choice 'D.' Choices A, B, and C are incorrect because they do not match the subject in number ('glass in three of the windows') and do not use the correct past participle form of the verb.