— Was the driving pleasant when you went to Mexico last summer?

— No, it ＿＿ for four days when we arrived, so the roads were very muddy.

A．was raining

B．had been raining

C．would be raining

D．rained

为了保证焊补修理质量，除严格要求焊补工艺外，还应（）。

A．由技术高的工人施焊

B．保证焊条质量

C．对零件待修表面进行清洁

D．焊前预热，焊后退火