The correct answer is A. Was broken.

1. Was broken: This option is correct because "one of the window panes" is a singular subject, so it requires the singular form of the verb "to be," which is "was." The sentence is in the past tense, so "was broken" correctly indicates that the action happened yesterday.

2. Is to be broken: This option is incorrect because it is in the future tense and indicates an action that is scheduled to happen, which does not fit the context of something that happened yesterday.

3. Were broken: This option is incorrect because "were" is used with plural subjects. Since "one of the window panes" is singular, "were" does not agree with the subject.

4. Have broken: This option is incorrect because "have" is used in the present perfect tense, which does not fit the past tense context of the sentence.

Summary:

- A. Was broken is the correct choice because it correctly matches the singular subject with the appropriate past tense form of the verb.