用CAD胡／CAM系统编制的三维曲面加工程序加工，球头刀的刀位点一般在球心。
参考答案：错
浆膜发生化脓性炎时，脓性渗出物大量蓄积于体腔内，称为（）
A.脓性卡他
B.脓性浸润
C.积脓
D.脓肿
E.蜂窝织炎
Mr. Liu told us that December 25 _____ Christmas Day. [ ]
A. is
B. was
C. has been
D. will be
