How many routes are there in the ordinary xyz-coordinate system from the origin to the point (i, j, k), where i, j, and k are positive integers, if we are limited to steps one unit in the positive x-direction, one unit in the positive y-direction, or one unit in the positive z-direction?

stratosphere: as the altitude increases, the air temperature increases. the stratosphere has a layer of ozone, called the ozone layer. this layer absorbs most of the ultraviolet radiation from sunlight. this results in the stratosphere being warmer.

i believe it's c. the trait for large beaks will be passed on to future generations through natural selection.

since eventually smaller beaks would have to find another source of food or even eventually just die out from the lack of food.