4. When a healthy young man stands up abruptly after lying down, the veins in the lower itmbs become distended and accumulate blood. Which of the following statements about the physiological conditions of the man is true? (Select the best answer from the choices given, and explain your answer.) (A) The capillary filtration in his leg will increase. (B) His stroke volume wiH increase (C) His heart rate will decrease. (D) Afferent activities of arterial baroreceptors will increase.