mark lives at sea level in miami, florida and is planning to hike pikes peak at an altitude of 14,000 feet. which of the following statements are true about the environmental differences between sea level and high-altitude environments? select all of the true statements. select one or more: a. at higher altitudes, the atmosphere has a reduced ratio of oxygen to carbon dioxide. b. regardless of elevation, the earth's atmosphere is always comprised of 21% oxygen. c. cities at sea level tend to have an average barometric pressure of 430 mmhg d. as altitude increases, barometric pressure decreases. e. as altitude increases, typical air temperature decreases. f. as partial pressure of oxygen decreases, it becomes more difficult for the body to deliver adequate oxygen throughout the body. g. reduced barometric pressure increases oxygen availability in the blood.