【多选题】一般常用的化学试剂分为基准试剂、优级纯、分析纯与化学纯四个等级。以下说法正确的是( )
B.
制备滴定液可采用分析纯或化学纯试剂,但不经标定直接按称重计算浓度者,则应采用基准试剂
C.
制备杂质限度检查用的标准溶液,采用优级纯或分析纯试剂
【判断题】In reality, it is quite difficult to follow the assessment principles.
【单选题】建筑物的耐久等级为二级时其耐久年限为( )年。
【单选题】There are some principles for us to follow when it comes to starting with a definition in the opening paragraph. Choose the one which is not correct.
A.
We’d better write a clear-cut and concise definition with key points.
B.
We’d better make the definition as extended as possible.
C.
We’d better use our own definition because it is uniquely created.
D.
We’d better write no more than three sentences for a definition.
【简答题】国际纯粹与应用化合会(IUPAC)将作为标准物质的化学试剂按纯度可以分为_______、_____、_______、________、______。
【简答题】( ) is the study of the rules or principles prescribed for people to follow when they use a language.