Which of the Following Correctly Describes the Technique Used in PNF

Which of the following correctly describes the technique used in PNF (Proprioceptive Neuromuscular Facilitation) ?

A) Passively moving the muscle in dynamic motion to increase flexibility.
B) A contract-relax sequence to relax the muscle stretch reflex mechanism.
C) Using muscle contraction of the extensors followed by muscle contraction of the flexors.
D) The required period of exercise for eliciting adaptation.