在轧制过程中，轧件打滑的实质是轧件的出口速度小于轧辊速度，这时整个变形区无（）。
A.前滑区
B.轧辊速度
C.轧制速度
D.后滑区
参考答案：A
预告信号机设于主体信号前方，对于进站信号、非自动闭塞的通过信号进行预告。
（71） analysis emphasizes the drawing of pictorial system models to document and validate both existing and/or proposed systems. Ultimately, the system models become the（72）for designing and constructing an improved system. （73） is such a technique. The emphasis in this technique is process-centered. Systems analysts draw a series of process models called（74） . （75） is another such technique that integrates data and processConcerns into constructs called objects.
A．Prototyping
B．Accelerated
C．Model-driven
D．Iterative
