What component of Earth's atmosphere exists entirely as a result of photosynthesis? A. oxygen gas, B. water vapor, C. nitrogen gas, D. carbon dioxide gas​

7th grade question (easy) look at the diagram of the food web. the arrows mean eaten by. what would happen if the number of snakes went down? answer choices are in the image.

What are some natural processes that represent physical and chemical changes?

Which of the following was not a major animal on land during the carboniferous period? amphibians insects both a and b none of the above