脑血管病的预防中最关键一环是（）
A.一级预防
B.二级预防
C.三级预防
D.四级预防
参考答案：A
---___________ everyone present at the meeting? ---No, all but one _________ there.
A．Was; was
B．Were; were
C．Was; were
D．Were; was
下列选项中属于不正常燃烧现象的是( )。
A．熄火、回火
B．脱火、回火
C．脱火、熄火
D．自燃、闪燃
