根据短文内容，选择正确答案。
C
    Mr. Brown lives in a nice house in a small town with his wife，Mrs. Brown. From Monday to Friday he works in an office near his house. He is free on Saturdays and Sundays. He has a nice garden beside his house. He likes growing flowers and he often works in the garden on Saturdays and Sundays. The flowers are very beautiful and Mrs. Brown likes them very much. She often helps Mr. Brown.

.已知函数是定义在R上的奇函数，且当时不等式成立， 若，，，则的大小关系是(       )

下列命题：①菱形的四个顶点在同一个圆上；②正多边形都是中心对称图形；③三角形的外心到三个顶点的距离相等；④若圆心到直线上一点的距离恰好等于圆的半径，则该直线是圆的切线。其中是真命题的有（      ）

分别用如图所示的两个滑轮组，将同一物体提升到相同高度．若物体受到的重力为100N，动滑轮的重力为10N．把物体匀速提升1m的过程中，（不计绳重和摩擦）下列说法正确的是(   )

以下有关元素性质的说法不正确的是（   ）