下列哪项可引起金属音调咳嗽
A.喉炎
B.声带炎
C.支气管癌
D.喉癌
E.百日咳
参考答案:C
Miss Jones is a () engineer than miss Smith.
A.BEST
B.bad
C.worser
D.worse
设n(n≥3)阶矩阵
若矩阵A的秩为n-1,则a必为______.