Evidence Has Been Obtained for the Hypothesis That Speech Production

Evidence has been obtained for the hypothesis that speech production is geared to achieve relative positions of the articulators to achieve appropriate acoustic results. Which of the following constitutes such evidence?

A) If the lower lip is gently and slightly pulled down while a speaker is about to say "p," the upper lip moves down at a higher than normal rate
B) If the lower lip is gently and slightly pulled down while a speaker is about to say "f," the upper lip does not move down at a higher than normal rate
C) Both b and c
D) If the lower lip is gently and slightly pulled down while a speaker is about to say "p" or "f," the upper lip moves down at the same rate