小林沿着一个圆形水池的外沿走了一周，正好走了50步，每步的距离约是0.628 米，这个水池的占地面积大约是（ ）平方米。
78.5
___ staying at hotels in Red River Village, tourists can help the villagers make money so that they
can take _____the river and the birds.
[ ]
A. By; care for
B. By; care of
C. Through; care about
D. With; care of
如果一个风险事件的发生机会是45次中出现15次，基于类似事件的经验，在下个项目上，这个风险事件发生的概率是多少？（）
A.90%
B.45%
C.15%
D.33%
