For the following numerical variables, state whether each is discrete or continuous.
a. The number of in sufficient-funds checks received by a grocery store during a given month
b. The amount by which a 1-pound package of ground beef decreases in weight (because of moisture loss) before purchase
c. The number of New York Yankees during a given year who will not play for the Yankees the next year
d. The number of students in a class of 35 who have purchased a used copy of the textbook