使用氧气－乙炔气焊设备焊接紫铜管时，一般选取（）.
参考答案：射吸式焊炬
A recent survey revealed that __________ dogs barking incessantly in the night that we disliked most.
A．was
B．there be
C．it was
D．there were
组成聚形的单形，必须具有（）对称型。
A.不同
B.相同
C.相似
D.同一晶系的
