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.
It was not until (A) the late 1970s when (B) these country people could enjoy (C) the benefits (D) of electricity.

A. not until

B. when

C. these country people could enjoy

D. benefits