Question

in 1948, the kyoto observatory completed its first detailed sky survey. by the time the data were published two years later, astronomers ___ more than 9,000 variable stars, establishing a foundation for future stellar mapping.

6 □ mark for review
which choice completes the text so that it conforms to the conventions of standard english?
① identifies
② had identified
③ have identified
④ would have identified

Explanation:

The sentence has a time reference "by the time the data were published two years later" (with "were published" indicating a past event). "By the time" + a past event calls for the past perfect tense (had + past participle) to show an action completed before another past action. Option A is simple present, incorrect. Option C is present perfect, wrong tense. Option D is conditional, not fitting. Option B "had identified" is past perfect, correct.

Answer:

B. had identified