关于一道管卫东数学题 很基本的一道题 我却不懂。谢谢NN来解答

我也不懂，还搜了一题
If the probability is 0.6 that stock A will increase in value during the next month and the probability is 0.4 that stock B will increase in value during the next month, what is the greatest possible value for the probability that neither of these two events will occur?

A) 0.20

B) 0.24

C) 0.40

D) 0.46

E) 0.60

貌似选B，那C呢？

为什么是B呢。我还是不懂。。
两支股票上涨如果相互独立 问题问两个都没发生的概率？
怎么算呢？