1D累计切角属于
A．Ⅰ类洞B．Ⅱ类洞C．Ⅲ类洞D．Ⅳ类洞E．Ⅴ类洞
参考答案：D
1，2，3，4，5共有5!种排列a1，a2，a3，a4，a5，其中满足“对所有k=1，2，3，4，5都有ak≥k-2”的不同排列有______种．
Do you know ____John is getting on well with his studies?
A．how
B．what
C．that
D．with
