Question

Use the past perfect continuous tense form of the verb in the following sentence:
Mary __________ at the school for at least a decade before she decided to move to another school.

• A. was teaching
• B. had been teaching
• C. had taught
• D. taught

Answer 1

The correct option is B had been teaching

Here, had been teaching in past perfect continuous is correct because it is used to indicate an action in the past that began before a certain point in the past and continued up untill that time. Here, 'teaching for at least a decade ....' indicates the usage of 'had been teaching'.
'Was teaching' in past continuous is incorrect because it is used to indicate uncompleted action in the past (with or without time reference).
'Had taught' in past perfect is incorrect because it is used to indicate a completed action of the past that happened before another event took place.
'Taught' in past simple is incorrect because it indicates an action that has already been completed.