6. All of the following statements are true regarding the muscles of the upper and lower mouth except
a. The muscles of the upper and lower mouth originate in different places, but they all insert on the mouth.
b. Many different muscles are necessary for speaking, eating, whistling, and performing other actions of the mouth.
c. The muscles of the upper mouth push the mouth downward, whereas the muscles of the lower mouth push the mouth upward.
d. The angle where the upper and lower mouth muscles attach to the mouth determine how they move the mouth.