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.
Also, it is very easy to take care of the bird unlike other species of parrots. Although the bird is a native of Australia, it is quite common to find cockatiels as pets all over the world. Usually in the wild, cockatiels either live in pairs or in a small flock. You will find them living quite close to water bodies. However, pet shops today supply cockatiels to anyone who is interested in owning this beautiful, friendly and intelligent bird.