下列属于用火作业的是（）。
A.砂轮机切割作业
B.铁锤敲击紧固或松动由壬接头
C.使用火炉、电炉
D.现场使用防爆对讲机
参考答案：A, B, C
Some people think clowns are only funny for children. _____________ , they can help people forget their problems, at least for a short moment.
A．Actually
B．Especially
C．Probably
D．Surely
材料的强度与塑性如何测定（检验）？
