下列哪项理论可被用于降低成本或缩短计划（）
A.赶工
B.变更范围
C.平等实施几项活动而不是按序列实施
D.以上都是
参考答案：D
Great changes _____ in my hometown since 1980. [ ]
A. have been taken place
B. took place
C. have taken place
D. were taken place
分油机要求其工作水的pH值应（）
A.小于11
B.大于4
C.小于5
D.大于6
