图解法通常用于求解有（）个变量的线性规划问题。
A.1
B.2
C.4
D.5
参考答案：B
封闭图形______就是这个图形的周长．
Don't laugh at _____. You should help them when they are in trouble.[ ]
A. other
B. the other
C. others
D. the others
