根据句意和汉语注释，写出单词的正确形式。

1.Audrey Hepburn was ____________(活跃的) in the film industry for nearly 40 years.

2.It will be a dangerous trip. Are you sure you want to take the _________(风险)?

3.I cannot ___________(许诺) you anything at this moment, but I will try my bestl.

4.The London Olympic Games , the ___________(第三十) summer games in history, will open on July 27th, 2012.

通过经营杠杆系数的计算可以说明（）。

A.销售变动所引起的每股收益的变动

B.在固定成本不变的情况下，经营杠杆系数越小，销售额越大

C.若销售额达到盈亏临界点时，经营杠杆系数趋于无穷大

D.经营杠杆系数总是大于1