—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.