It's reported the Olympic flame for 2008 Beijing Games ________ Beijing International

Airport on March 31, 2008. [ ]

A. reached to

B. arrived at

C. got at

D. entered in

两根细长压杆，材料及约束情况均相同，截面尺寸分别如图5-8-4a和图b所示，则图b压杆的临界荷载是图a的（）倍。

A．2

B．4

C．8

D．16