将黏土刻成一个个单子,烧硬后用于排版印刷,印完一版,单字可卸下以备再用。此项技术最早记载于()
A.《史通》
B.《农政全书》
C.《农书》
D.《梦溪笔谈》
参考答案:D
______ do you sleep every night? More than eight hours. [ ]
A. How often
B. How much
C. How long
D. How many
焊接的分类中,自动化焊接分为波峰焊和()。
A.接触焊
B.熔焊
C.软焊