A polling company has been hired to determine the approval rating for a local member of Congress. The company completed the poll by creating a survey and instructing representatives to stand outside a mall to give the survey to departing shoppers. The polling representatives were also instructed to take responses only from participants who were male. Then, the polling company published a report which put the congressperson's approval rating at 79%. Why could this sample be biased?

A. The representatives of the company were male.

B. The mall was outside the congressperson's local area.

C. The survey questions were biased toward the congressperson's opponent.

D. The representatives of the company only gave the survey to a select group, as opposed to a wider, more representative sample.