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
解析:可联系答.案.网客服索取。