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
