An opinion research firm wants to find the country's reaction to a speech by a famous politician. they randomly select six states, then randomly select ten zip codes from each state. fifty people from each zip code are randomly selected for the survey. this is an example of

This above passage describes random sampling. Because the researchers pick six random states, then ten random zip codes (for a total of 60 zip codes), then 50 people from each zip code (for a total of 50*60 people), the process is completely random. Although, I would probably make an alteration to include 3 states that favor one party, 3 states that favor another party, and 3 swing states for a survey like this (with everything still being random).