下列污染现象主要与SO2有关的是（ ）
A．臭氧空洞
B．酸雨
C．光化学烟雾
D．温室效应
答案：B
运输问题的数学模型中包含（）个约束条件。
A.m*n
B.m+n
C.m+n-1
D.m*n-1
The main feature of (72) is that they follow a first-come/first-served rule. For instance, the line of (73) waiting to be run on a computer system.
A．works
B．jobs
C．tasks
D．assignments
