DFD中的每个“加工”至少需要______。
A.一个输入流
B.一个输出流
C.一个输入流或一个输出流
D.一个输入流和一个输出流
参考答案:D
He has a friend who ____ the piano very well. [ ]
A. play
B. playing
C. plays
D. played
计算筒仓的水平地震作用及自振周期时,取贮料总重的(),作为贮料的有效重力,其重心可取贮料总重的重心。
A、60%
B、70%
C、80%
D、90%