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 sentence that best combines each pair of sentences in the following questions.
He turned the radio on at 7.30. He was still listening to it when his mother came home at 9.00

A. He has been listening to the radio at 7.30

B. He had been listening to the radio since 7.30

C. He has been listening to the radio after 7.30

D. He had been listening to the radio by 7.30