Identify the type of sampling (random, systematic, convenience, stratified, cluster) used when a sample of people who smoke is obtained as described below.
a) A complete list of all smokers is somehow compiled and every 1000th name is selected
b) At the next New York City marathon, a survey is conducted of all runners.
c) Fifty different grocery store owners are randomly selected, and all of their customers are surveyed.
d) A computer file of all smokers is compiled and they are all numbered consecutively, then a random numbers generated by computer are used to select a sample of 1000 smokers.
e) All of the smokers' zip codes are collected, and 5 smokers are randomly selected from each zip code.