管子的焊接包括哪些部分？
参考答案：
管子的焊接包括制作管子坡口、对口、施焊、焊后热处理及焊后检查。
______, but he insisted that he _____ to school ．
A．Though he was ill , went
B．He was ill, go
C．Having been ill, should go
D．Having been ill , went
生物的______作用就是一种生物通过向体外分泌代谢过程中的化学物质，对其他生物产生直接或间接的影响。
