室颤最常见的病因是()
A.休克
B.心肌病
C.冠心病
D.心瓣膜病
E.预激综合征合并房颤
参考答案:C
(x+1)(x-1)-1=( ),4-9x2=( )( )。
The mountain is about 6300 meters _________. It is quite difficult to reach the top of it.[ ]
A. tall
B. high
C. long
D. far