The nurse is teaching the mother of an infant with tetralogy of Fallot. The mother asks what to do when her infant becomes very blue and has trouble breathing after crying. The nurse should tell the mother（）
A. "Leave the infant alone until the crying stops. "
B. "Put the infant in the knee-chest position. "
C. "Offer the infant a bottle of formula. "
D. "Take the infant for a ride in the car. "
