Researchers want to collect cholesterol levels of U.S. patients who had a heart attack two days prior. The following are different sampling techniques that the researcher could use. Classify each as simple random sample, stratified sample, systematic sample, cluster sample, or convenience sample.

a.)The researchers randomly select 5 hospitals in the U.S. then measure the cholesterol levels of all the heart attack patients in each of those hospitals.

b.)The researchers list all of the heart attack patients and measure the cholesterol level of every 25^th person on the list.

c.)The researchers go to one hospital on a given day and measure the cholesterol level of the heart attack patients at that time.

d.)The researchers list all of the heart attack patients. They then measure the cholesterol levels of randomly selected patients.

e.)The researchers divide the heart attack patients based on race, and then measure the cholesterol levels of randomly selected patients in each race grouping.