a sum of money paid regularly to an insurance company to protect sb. against some risk of loss or damage The employers make the employees pay for a large portion of their health insurance p .
【简答题】给出下列四个命题: ①函数 f ( x )=ln x -2+ x 在区间(1 , e )上存在零点; ②若 ,则函数 y = f ( x )在 x = x 0 处取得极值; ③若 m ≥-1,则函数 的值域为 R ; ④“a=1”是“函数 在定义域上是奇函数”的充分不必要条件。 其中正确的是 。