Topic: Sequence of Tense,

Best Answer Explained in Below-:

The correct answer to the sentence completion is "C) had broken." This choice employs the past perfect tense, which indicates that an action occurred before another point in the past. In the context of the sentence, "When we arrived at the shop," this arrival is the first event in the past timeline. The use of "had broken" suggests that the action of someone breaking into the shop happened prior to their arrival.

The other options do not fit as well within the temporal structure of the sentence. Option A, "broke," is simple past tense and does not clarify the sequence of events; it suggests the action happened simultaneously with their arrival, which is illogical in this context. Option B, "would break," introduces a conditional future aspect that doesn't apply, as the context relates to past events. Lastly, option D, "had been breaking," implies an ongoing action that started before their arrival, but it lacks the conciseness needed to describe a completed action, which is more suitably conveyed by "had broken."

In summary, "had broken" effectively establishes the sequence of events, making it the best choice for the completion of the sentence.