强调预防作用的控制方法是（）
A.现场控制
B.反馈控制
C.前馈控制
D.间接控制
参考答案：C
MPEG的帧间编辑采用（）方式。
A.I帧
B.P帧
C.E帧
D.B帧
"It was fortune that paid me a visit ____," said the modest professor at the award ceremony. [ ]
A. by mistake
B. by chance
C. in order
D. in place
