单侧嗅觉丧失提示脑脊液鼻漏位于()
A.额窦后壁
B.鼻窦
C.鞍结节、蝶窦、后组筛窦
D.筛板
E.颅中窝
参考答案:D
16.—Where is Lily, Lucy? I cannot find her anywhere.
—She_________have been off long. I saw her clean the window just now.
A.shouldn’t
B.can’t
C.mustn’t
D.needn’t
简述信用产生的原因。