各个螺纹的连接应用密封胶带或螺纹密封脂密封。
参考答案:对
— Sorry, Professor Smith. I didn't finish the assignment yesterday.
— Oh, you( )have done it as yesterday was the deadline. [ ]
A. Should
B. mustn't
C. must
D. shouldn't
下列实验方法合理的是( )
A.可用水鉴别NH4Cl、NaOH、NaCl三种固体
B.可用铁粉除去FeCl2溶液中的少量的CuCl2
C.可用澄清石灰水鉴别Na2CO3溶液和NaHCO3溶液
D.为准确测定盐酸与NaOH溶液反应的中和热,所用酸和碱的物质的量必须相等