Ineed !

a polygon is a pentagon if and only if it has five sides."

if this statement is true, then which of the following statements must also be true?

a. a polygon is not a pentagon if and only if it does not have five sides.
b. a polygon is not a pentagon if and only if it has five sides.
c. a polygon is a pentagon if and only if it does not have five sides.
d. a polygon does not have five sides if and only if it is a pentagon.