浇注系统一般由哪几部分组成,各有何作用?
参考答案:
外浇口:承接金属液缓冲液流压力
直浇道:调节液流压力和流速
横浇道:阻挡缺陷和杂质进入型心
内浇道:分配液流余量和充型
—I think it’s very dangerous to drive six hours without a rest.
—I agree. Six hours really a very long time.
A.has
B.is
C.were
D.am
中国出入境检验检疫产生于20世纪中期。