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:

Câu 29: She turned the radio on at 7.30. She was still listening to it when her mother came home at 9.00.

     A. She has been listening to the radio at 7.30.

     B. She had been listening to the radio since 7.30.

     C. She has been listening to the radio after 7.30.

     D. She had been listening to the radio by 7.30.