(1)求;
(2)设炸药爆炸时释放的化学能为且完全转化为两小球动能,求从爆炸到发生第
一次碰撞的时间t。
(1)(2)
— 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