- Do you often hear John _______ in his room?

-Listen! Now we can hear him ________ in his room.[ ]

A. sing, to sing    

B. singing, singing    

C. sing, singing    

D. to sing, singing

如果鼻、咽、喉受感染，其中的病菌可能通过（）进人中耳，引发中耳炎。