按照焊接过程中金属所处的状态及工艺的特点，可将焊接方法分为( )。
A．熔化焊
B．压力焊
C．气割
D．钎焊
参考答案：A,B,D
_____their students, the famous teacher came into the hall.
A．Followed
B．Followed by
C．Being followed
D．Having been followed
若将低倍镜下的物像转换高倍物镜下观察时，可直接转动转换器。( )
