What does "dirty pool" at the end of the second paragraph mean

A．The stories of Harry Potter are criticized in some other cities in U.S except New Mexicon
B．Young people are fascinated with Harry Potter
C．Christian churches hate Harry Potter
D．Pastor Jack Brock planned to burn the Harry Potter books on Sunday

A．separate it
B．use 3-D tech
C．put something in it
D．remove something from it