气体类危险化学品泄漏事故现场，要关闭前置阀门切断泄漏源。
参考答案：对
—How much _______ this pair of trousers?
—Ten dollars _______ enough.[ ]
A. are; is
B. is; are
C. are; are
D. is; is
脑血栓形成患者服用阿司匹林，目的是（）
A.退热
B.抗风湿
C.扩张脑血管
D.抗血小板聚集
E.防止头晕
