NO.PZ2020010303000003
问题如下：
What type of events are Poisson random variables used to describe?
选项：
解释：
Poisson random variables are used for counts—the number of events in a fixed unit for time. For example, the number of mortgage defaults over a month.
没看懂答案的意思，能翻译一下吗？上课老师讲的是n非常大，p很小时用泊松分布
