Hi, got this question from the MGMAT SC Guide but no OA provided, please help! Thanks!

When he phones her, [u]she tells him to stop calling, but he acted as if he had not understood her.[/u]

A. same
B. she told him to stop calling, but he acted as if he had not understood her.
C. she tells him to stop calling, but he acts as if he did not understood her.
D. she tells him to stop calling, but he acts as if he has not understood her.
E. she tells him to stop calling, but he acted as if he does not understand her.