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.
We purchased our cockatiel Charlie 23 years ago. At the time we got 3 cockatiels, a male that I fell in love with and Charlie and a female who quickly became a bonded pair for my Mother. Mom wanted Charlie because she felt sorry for him, he had been injured in transport from a hatchery in FL. to our ben franklin store in IA. His feathers on his neck never grew back.