Final answer:
The tense of the underlined verb 'had been attending' is past perfect progressive, indicating an ongoing action in the past that ended before another one.
option 'd' is the correct
Step-by-step explanation:
The student asked about the tense of the underlined verb in the sentence "Rockwell had been attending the New York School of Art when he dropped out and enrolled at the National Academy of Design.
The correct tense for the underlined verb "had been attending" is past perfect progressive. This tense is used to express an action that was ongoing in the past and was completed before another past action. In this case, Rockwell's ongoing attendance ended when he decided to drop out and enroll in another school.
The past perfect progressive tense is structured with the past perfect of the verb "to be" (had been) plus the present participle (attending) of the main verb. It's used to emphasize the duration of the past action before another action in the past.