It's hard to trackblue whale in that ocean which has been killed off by commercial whalin

问题补充：

Its hard to trackblue whale in that ocean, which has been killed off by commercial whaling and is now listed asendangered species.

A. the; the

B. the; 不填

C. a; 不填

D. the ; an

答案：

A. the; the

B. the; 不填

C. a; 不填

(答案→)D. the ; an

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