起钻时,外钳工趁司钻刹车时取出保险销,拉出吊环,()挂人井口承载吊卡,插好保险销。
A.一次
B.两次
C.三次
D.四次
参考答案:A
We laugh at jokes,but seldom____________about how they work.
A.we think
B.think we
C.we do think
D.do we think
对喉镜检查,气管和支气管手术及支气管胸膜瘘的病人易采取
A.PCVB.SIMVC.PEEPD.CPAPE.HFV