Identify the following sample designs:
a. The names of 200 patrons of a casino are drawn from a list of visitors for the last month, and a questionnaire is administered to them.
b. A radio talk show host invites listeners to call in and vote yes or no on whether handguns should be banned.
c. A dog food manufacturer wants to test a new dog food. It decides to select 100 dog owners who feed their dogs canned food, 100 who feed their dogs dry food, and 100 who feed their dogs semi-moist food.
d. A poll surveys men who play golf to predict the outcome of a presidential election.