Since 2005, a 50-acre chunk of hillside — almost eight million cubic y

VERITAS PREP OFFICIAL SOLUTION:

This sentence contains an unusually structured element within the dashes that can easily distract you from what really matters in getting the problem correct: tense. A close look at the answer choices shows the important decision point between “had been sliding,” “has been sliding,” and “slid.” When “since” is used in a sentence, it generally must be linked with the present perfect tense.

For instance, it is always incorrect to say, “Since 2005, John lived in California” and it is incorrect to say, “Since 2005, John had lived in California” unless you know that the action stopped at some point in the past. This sentence begins with “Since 2005...” and it is clear from the independent clause after the semi-colon that the action continues into the present.

As a result, only (D) can be correct as the past perfect “had been sliding” in (A), (B), and (C) and the simple past “slid” in (E) all create illogical timelines (the action did not stop at some point in the past). While the correct answer uses several appositive phrases to create an unusual structure between the dashes, it is the only one with the correct tense, so you should not spend time considering the other differences. Correct answer is (D).