下列哪一种状态属于承载能力极限状态（）
A、雨蓬倾覆
B、钢梁有较明显的变形
C、拉杆在动荷载下剧烈晃动
D、吊车梁在吊车行驶时发生抖动、摇晃
参考答案：B
旅游者在购买航空客票后，如因种种原因需要退票，则应( )退票。
A．在任意航空售票点
B．到机场机票售票处
C．到开出航空客票的票务处
D．找到出票人
Which of the following statements regarding the mark to market of a futures account is FALSE Marking to market of a futures account:()
A. may result in a margin balance above the initial margin amount and may be done more often than daily.
B. is only done when the settlement price is below the maintenance price.
C. effectively adjusts the price of the future to the new equilibrium level.
