Select the statement in if-then form.
An acute angle measures less than 90 degrees
a. If an angle is an acute angle, then the angle measures less than 90 degrees.
b. If an angle is not an acute angle, then the angle measures less than 90 degrees.
c. If an angle measures less than 90 degrees, then it is an acute angle .
d. If an angle measures less than 90 degrees, then it is not an acute angle .