进行一般银焊时，火焰之调整宜采用何种方式（）
A.氧化焰
B.中性焰
C.还原焰
D.以上均可
参考答案：B
__________said that some foreigners will come to our school.[ ]
A. They are
B. They were
C. That is
D. It is
对于天然建筑材料的详查阶段，勘察储量一般不小于设计需要量的( )倍。
A．2
B．3
C．4
D．5
