有凝结盖的铁水罐,不应鼓盖操作用氧烧盖时,专用胶管和钢管应不短于()m,管接头无泄漏,防止回火。
A. 10
B. 5
C. 8
D. 4
学习与课外
For this part, you are allowed 30 minutes to write an essay on how to balance academic study and extracurricular activities。 You should write at least 150 words but no more than 200 words。
下面是一些聚合物或辅助剂名称:①Polyethylene glycol 400。②Polysorbate 20=Polyoxyethlene 20 Sorbitan monolaurte。③Carboxymethylcellulose sodium sodium 12。④Polyvinyl alcohol 17B88。试说明以上各名称中数字的意义。