圆的周长÷直径=π（一定），是比值一定，圆的周长和直径成正比例．
故选：B．
139. --- How did you spend you summer vocation?
--- I went to Beijing and stay there for fortnight.
The underlined part probably means _____.
A．one week
B．two weeks
C．four days
D．three weeks
从系统的观点来看，局部计划的最优化，对全局来说是最合理的。 ( )
