题干
In April, the weather in some places in Shanxi was really changeable. People still remember they have _______ four seasons in a week.
A：organized
B：experienced
C：described
D：travelled
答案(点此获取答案解析）
B
，
表示不超过
的最大整数，如
. 定义
上的函数
，若
，则
中所有元的和为（ ）