问题如下：
Recently Analyst Bob is studying regulatory environment in a country. 4 years ago, the country advocates environment-friendly power generation. So the government increases taxes on coal fuel and provides subsidies on solar power and wind power generation. Bob finds some changes in electricity generation production as following table shows.
According to the table, which government policy is most effective?
选项：
A.Coal fuel.
B.Solar power.
C.Wind power generation.
解释：
A is correct.
考点：Tools of regulatory intervention
解析：首先我们根据表格计算一下政府实施政策后，不同发电来源产电的变化
从计算结果看，煤炭发电降低了10.84%，太阳能发电增加了7.67%，风力发电增加了9.43%。因此从环保节能的角度而言，煤炭发电加税政策收到的效果最大。
本题可以参照老师上课所讲的例题，算出每年的年平均增长率，然后选取上升或者下降幅度最大的么
