塔式起重机按照（）分上回转达和下回转。
A.有无行走机构
B.回转达方式
C.安装形式
D.骨料裂缝
参考答案：B
经观测，某时某地海拔高度10m和30m处的气温分别为297.8K和297.5K，则两个高度之间的大气稳定度是（）。
Which of the following statements regarding an option prior to expiration is TRUE The maximum value of:()
A. a European put is less than the maximum value of an American put.
B. an American call is less than the maximum value of a European call.
C. a European put is equal to the maximum value of an American put.
