7. During strenuous exercise, skeletal muscles use up and produce large amount of , which causes pain and fatigue in the muscle. A. Oxygen, lactic acid C. CO2, pyruvic acid
B. Pyruvic acid, lactic acid D. Pyruvic acid, CO2

Which conditions need to be in balance for cells to function? check all that apply. blood sugar food intake body water body temperature body mass

What is the problem in this article? what solution does the article propose?

Which statement describes how favorable traits in a population relate to natural selection? they are the only traits that ever exist in the population. they build in the population over time. they are rarely passed on to offspring. they are found only in a few individuals within the population.