Please help me ... I am stuck on this since forever

A study to determine the opinion of Americans about the use of marijuana for medical purposes is being conducted using the following designs. Categorize the sampling method as a simple random sample, stratified sample, cluster sample, quota sample, systematic sample, or convenience sample. ( a) The researchers divide Americans into groups based on the person's race, and then take random samples from each group proportionally. (b) The researchers call every 2000th person in a database of U.S. adults provided by the U.S. Census Bureau. (c) The researchers put ads on commonly used social media sites that link to a survey