13只鸽子飞回4个鸽笼，至少有4只鸽子要飞进同一个鸽笼里。为什么？
解：13÷4=3……1
答：至少有4只鸽子飞进同一个鸽笼里。
小强用50N的水平拉力向右拉小车，在图中画出拉力的图示．
— Must I take a bus?
— No, you _____ . You can walk there. [ ]
A. must not
B. don't
C. don't have to
D. had better
