To complete the sentence with the past perfect form of the verb "teach" in the context given, you would say:
"Mrs. Kramer had taught ninth-grade geography at Montgomery High before leaving to pursue a master's degree in cartography."
In this sentence:
1. "Had taught" is the past perfect form of the verb "teach" because it indicates an action that was completed before another past action.
2. The use of "had" before the past participle "taught" signals that the teaching occurred before Mrs. Kramer left to pursue her master's degree.
3. The past perfect tense helps clarify the sequence of events, showing that the teaching took place prior to her departure for further studies.
