We couldn't solve the problem until our teacher arrived.

Câu hỏi: Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions
We couldn't solve the problem until our teacher arrived.
A. Not until we solved the problem could our teacher arrive.
B. When our teacher arrived, we solved the problem.
C. Until our teacher arrived, we were able to solve the problem.
D. Not until our teacher arrived could we solve the problem.