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.
Except for the Budgerigar, the Cockatiel is rated as the most popular and widely kept of the approximately 340 species of the order of psittacine birds. They are a hardier bird than their rival, the Budgie, and have a life span of 15 to 20 years versus the Budgie's 7 to 8. They are gentle and sociable by nature and have pert, bright personalities. They quickly pick up words and phrases and especially love to whistle.