What type of web sites are posted by activist groups such as the Sierra Club and the National Rifle Association?

The answer is "Advocacy".

Explanation:

The advocacy websites provide an effect on the judgment, which is about policy making and distribution of power across government, economic and environmental power structures.

It will lead to better facilities and improved health. It guarantees that sometimes the required change happens, it is a part of both organizations, that's why the "Advocacy" is the correct answer.