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.
Some cockatiels, especially some lutinos and other color mutations bred for the pet trade, tend to be rather smallboned birds. For these birds, a weight between 78 and 90 grams may be average. Cockatiel breeders that are selectively breeding their birds for showing in competition will usually have larger birds. They tend to be longer and more solid in appearance, and often weigh between 110 and 125 grams.