TV set is one of in the world.A. most useful inventionB. the most helpful inventions C. mo

问题补充：

TV set is one of in the world.

A. most useful invention

B. the most helpful inventions

C. more helpful inventions

D. less useful invention

答案：

A. most useful invention

(答案→)B. the most helpful inventions

C. more helpful inventions

D. less useful invention

解析：句意：电视机是世界上最有用的发明之一。这里one of+可数名词的复数，故排除AD；这里用了最高级所以它的前面应该用定冠词修饰。故选B。