单项选择题

Beethoven knew that he was going deaf ________.
[A] when he could not hear himself humming a tune [C] when the humming noise grew louder
[B] when he heard a humming noise [D] when the doctor told him

A.Beethoven knew that he was going deaf ________.
B.when he could not hear himself humming a tune
C.when he heard a humming noise
D.when the humming noise grew louder
E.when the doctor told him