SFC步进顺控图中按流程类型分主要有（）。
A.简单流程
B.选择性分支
C.并行性分支
D.混合式分支
参考答案：A, B, C, D
Look! There is a crowd of people over there. Go and see what ________ and if it is a bargain, buy it. [ ]
A. has been selling
B. has been sold
C. is selling
D. is being sold
王建老师认为，台东地区出现的水向上流的情况是受到（）的影响。
A、视觉差异
B、重力
C、地形
D、气候
