Which of These Statements Does NOT Describe Cross Bridges

Multiple Choice

Which of these statements does NOT describe cross bridges

A) They are the globular heads of myosin molecules.
B) They have actin binding sites that are normally covered by troponin and tropomyosin, except during excitation-contraction coupling.
C) They bind with actin and then bend to pull the thin filaments inward during contraction according to the sliding filament mechanism.
D) They require Mg2+ to bind ATP to them.