当使用环境的氧浓度及毒害气种类不明或不稳定时，应选用自给式呼吸器。
参考答案：对
------What do you think of her?
------I thought her nice and honest I met her.
A．the first time
B．for the first time
C．first time
D．by the first time
既能和解退热，又能升阳举陷的药物是（）
A.葛根
B.柴胡
C.黄芪
D.升麻
E.桔梗
