球墨铸铁电弧冷焊,当施工环境气温低且焊件大时,焊前需预热至()。
A、50℃
B、100~200℃
C、400℃
D、600~700℃
参考答案:B
all day, I went to bed early.
A.Working hard
B.Worked hard
C.Having worked hard
D.To work hard
简说刘禹锡咏史诗的特点。