Answer:
The government function selected is protection and regulation of the enviroment.
This government function is mainly carried out by the Enviromental Protection Agency (EPA).
Over the past fifteen years, the EPA annual budget has averaged at around 8 billion dollars. In this time frame, it had its highest budget in 2010, with over 10 billion dollars.
The EPA essentially deals with market failures. Externalities like pollution or over exploitation of natural resources (tragedy of the commons) are some of the most commonly issues that the EPA has to solve.