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.
The biggest sign that your pet cockatiel might be sick is a change in behavior. A healthy pet bird is active and alert: eating, playing and vocalizing. A pet cockatiel that sleeps a lot or sits fluffed up in the corner of the bird cage could be sick. If there is even a slight change from normal cockatiel behavior or if your cockatiel shows other signs of illness, your pet bird could be sick. If your pet cockatiel is sick then take it to an avian veterinarian as soon as possible. In general, cockatiels (and all pet birds, as well as wild parrots) do not show obvious signs of illness. This is a defense mechanism. In the wild, a sick bird or parrot is a target for predators, so all birds (wild birds and pet birds) do everything they can to mask their sickness.