若函数在x=0处连续，则（）

设 f(x) 和 F(x) 分别是随机变量X 的分布密度函数和分布函数，则对任意a<b，有()

袋中有 3 个红球， 2 个白球，第一次取出一球后放回，第二次再取一球，则两球都是红球的概率是 ( )

若线性方程组AX=0只有零解，则线性方程组AX=b( )．

向量组的秩是 ( )．

设 A，B 都是 n 阶矩阵 (n>1) ，则下列命题正确的是( )．

For the new country to survive, ________ for its people to enjoy prosperity, new economic policies will be required.

She had clearly no ________ of doing any work, although she was very well paid.

The wealth of a country should be measured ________ the health and happiness of its people as well as the material goods it can produce.

When workers are organized in trade unions, employers find it hard to lay them ________.