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.
Peter heard a strange sound on the roof. He became very frightened.
A.On hearing a strange sound on the roof, Peter became very scared.
B.He became very frightened after he heard a strange sound on the roof.
C.He heard a strange sound on the roof and then becoming very terrified.
D.Peter became very frightened so he heard a strange sound on the roof.