预热有哪些作用?
参考答案:
预热能降低焊后冷却速度,预热可以减小热影响区的温度差别,在较宽范围内得到比较均匀的温度分布,有助于减小因温度差别而造成的焊接应力。
项目实施结果评价,一般在工程咨询单位提供咨询服务的项目建成投产()年后进行。
A.1
B.2
C.3
D.4
—Does Bob have vegetables for dinner?
—______. But his sister has some carrots.
A.Yes, he has
B.No, he hasn’t
C.Yes, he does
D.No, he doesn’t