What Is the Difference Between a Pop-Up and Pop-Under Ad

Multiple Choice

What is the difference between a pop-up and pop-under ad?

A) A pop-up ad appears when you open a Web site;you do not see a pop-under ad until you close your current browser window.
B) A pop-up ad uses a separate window;a pop-under ad does not.
C) A pop-up ad is a click-and-order ad;a pop-under ad is considered a click through ad.
D) A pop-under ad is a type of spyware;a pop-up ad is not.