—When do you ________?
—At four o'clock.[ ]
A. leaving
B. leave
C. leaves
答案：B
A={1，2，3，4，5}，B={6，7，8}从集合A到B的映射中满足f（1）≤f（2）≤f（3）≤f（4）≤f（5）的映射有______个．
