简述焊接时，防止氢进入焊缝的主要措施？

A. who are you?
B. don't ask me.
C. I don't know.
D. would you please ring them up this afternoon?

A. 多尿期
B. 恢复期
C. 发热期
D. 低血压休克期
E. 少尿期