用面向对象方法设计了一个父类File和两个子类DiskFile和TapeFile，这两个子类继承了其父类的open方法，并给出不同的实现。不同的子类执行open方法时，有不同的行为，这种机制称为（）。
A.继承
B.多态
C.消息传递
D.关联

在常见输入/输出接口中，USB接口速度快，设备安装配置容易，但不支持热拔插。

在计算机系统中，总线宽度分为地址总线宽度和数据总线宽度。若计算机中地址总线的宽度为32位，则最多允许直接访问主存储器（）的物理空间。
A.40MB
B.4GB
C.40GB
D.400GB

以下关于用例图的叙述中，不正确的是（）。
A.系统用例图反映了整个系统提供的外部可见服务

B.系统用例图对系统的协作建模

C.用例图主要包含用例、参与者及其之间关系三个要素
D.系统用例图对系统的需求建模

Software entities are more complex for their size than perhaps any other human construct,because no two parts are alike（at least above the statement level）.If they are,we make the two similar parts into one,a（1）,open or closed.In this respect software systems differ profoundly from computers,buildings,or automobiles,where repeated elements abound.Digital computers are themselves more complex than most things people build;they have very large numbers of states.This makes conceiving,describing,and testing them hard.Software systems have orders of magnitude more（2）than computers do.Likewise,a scaling-up of a software entity is not merely a repetition of the same elements in larger size;it is necessarily an increase in the number of different elements.In most cases,the elements interact with each other in some（3）fashion,and the complexity of the whole increases much more than linearly.The complexity of software is a（an）（4）property,not an accidental one.Hence descriptions of a software entity that abstract away its complexity often abstract away its essence.Mathematics and the physical sciences made great strides for three centuries by constructing simplified models of complex phenomena,deriving,properties from the models,and verifying those properties experimentally.This worked because the complexities（5）in the models were not the essential properties of the phenomena.It does not work when the complexities are the essence.Many of the classical problems of developing software products derive from this essential complexity and its nonlinear increases with size.Not only technical problems but management problems as well come from the complexity.
4、____
A.surface
B.outside
C.exterior
D.essential

为验证某呼叫中心是否能够承受大量呼叫信息同时呼入并得到正确处理，测试工程师一般采用（）测试工具。
A.负载压力
B.代码
C.网络仿真
D.故障诊断