Which of the following is TRUE regarding vascularity of lung?

Gravity has a relatively marked effect on the pulmonary circulation. In the upper pa of the lungs, the blood flow is less, the alveoli are larger, and ventilation is less than at the base. The O2 deficiency apparently acts directly on vascular smooth muscle in the area to produce constriction, shunting blood away from the hypoxic area. The ratio of pulmonary to systemic vascular resistance is usually less than 0.3. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 34. Introduction to Pulmonary Structure and Mechanics. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.