水的流速越大,金属腐蚀越快。()
参考答案:错
John said he had been working in the office for an hour, _______ was true.
A.he
B.this
C.which
D.who
刀具材料应具备良好的焊接性能,切削加工性能和()性能。
A.热处理
B.工艺性
C.耐磨性
D.耐热性