A. The pressure is lower as you gain altitude because there are more molecules of oxygen and nitrogen. B. The pressure is lower as you gain altitude because there are less molecules of oxygen and nitrogen. C. The pressure is the same because there is no change in the number of molecules.
The price of a cockatiel depends on a few factors. Firstly the price depends on whether or not the bird is tamed. For a tamed cockatiel it would cost around $80 - $120 and a untamed cockatiel would cost $15-$30 (AUS) Also the colouring of the cockatiel plays a part in the cost of the bird, as more rare colours (such as lutino or pearl cinnamon) may increase the cost of the cockatiel.
Even though your cockatiel is a warm-weather bird, she cannot withstand extreme heat any better than she can tolerate extreme cold. Never leave a cockatiel in a car, even when the weather is temperate outside, for instance. If you take the cage out on the patio during the spring or summer, don't place her in a spot with direct sunlight. Doing so can put her in danger of overheating, dehydrating and possibly dying.