换热器切换正确的是()
A.停换热器时,应先关冷流体,再关热流体
B.开时先通热流体,后通冷流体
C.开时先通冷流体,后通热流体
D.开时,冷流体和热流体同时打开
参考答案:C
He thought about ______Greece or Spain for vacation.
A.go to
B.to go to
C.going to
D.going
常用于胃癌检测的主要标志是()
A.CA153
B.CA125
C.CA724
D.SA
E.CA199