-I'll ask the teacher about the attributive clause. I'm very puzzled about it.

-That's just ________ most of our classmates have doubt.[ ]

A．what  

B．why

C．where  

D．how

最能明确诊断的辅助检查是

A．腰穿、脑脊液检查

B．腰椎MRI

C．下胸段MRI

D．中胸段MRI

E．头颅MRI