CO2气体保护焊,氮气孔产生的原因是______或______。
参考答案:保护不良;CO2气体不纯
若用明胶培养基培养细菌,其目的在于观察细菌能否液化明胶,则应在何温度培养()
A.30℃
B.25℃
C.22℃
D.35℃
E.37℃
System analysis is traditionally done top-down using structured analysis based on (1). Object-oriented analysis focuses on creation ofmodels. The three types of the analysis model are (2). There are two substages of object-oriented analysis. (3) focuses on real-world things whose semantics the application captures. The object constructed in the requirement analysis shows the (4) of the real-world system and organizes it into workable pieces. (5) addresses the computer aspects of the application that are visible to users. The objects are those which can be expected to vary from time to time quite rapidly.
空白(2)处应选择()
A.function model,class model and state model
B.class model,interaction model and state model
C.class model,interaction model and sequence model
D.function model,interaction model and state model