39. Which of the following is true about Piezol?
(A) Piezol lets out a chemical to help brain cells grow and regenerate.
(B) Piezol rubs out the surface of brain cells and gets them younger.
(C) Piezol is a special chemical that gives signals to brain cells.
(D) Piezol is a kind of protein that can detect the brain stiffness or softness.