Mark the letter A, B, C, or D on...

Câu hỏi: Mark the letter A, B, C, or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.
A vast quantity (A) of radioactive material (B) is (C) made when a hydrogen bomb explode (D).

A. a vast quantity    

B. material   

C. is     

D. explode