题目

—I haven't got a partner__ __． —Maybe you can ask John for help. A．work with  B．to work C．working with  D．to work with 答案：D有A、B两个口袋，A袋中装有4个白球，2个黑球，B袋中装有3个白球，4个黑球．从A、B两袋中各取2个球交换后，求A袋中有4个白球的概率．