题目

Every possible means _________ to prevent the spread of disease. A. have tried              B. have been tried        C. has tried   D. has been tried 答案：D若⊙P的半径为5，圆心P的坐标为（3，4 ），则平面直角坐标系的原点O与⊙P的位置关系是A.O在⊙P内B.O在⊙P上C.O在⊙P外D.无法确定