如果双侧喉返神经麻痹。突出的症状是()
A.声嘶
B.呛咳
C.呼吸困难
D.吞咽困难
E.喉喘鸣
参考答案:C
No one can________how the election will turn out, as there are many unknown facts. [ ]
A. protect
B. prepare
C. prevent
D. predict
设直线方程为
,则该直线必定( )。
A.过原点且垂直于x轴
B.过原点且平行于x轴
C.不过原点,但垂直于x轴
D.不过原点,且不平行于x轴