What was the initial atmosphere on Earth composed of? A. Hydrogen and Helium
B. Argon and Water vapor
C. Carbon dioxide and Sulfur
D. Nitrogen and Oxygen

All cells need water to survive. in order to maintain the necessary amounts, water can flow across the cell membrane from areas of higher concentration to areas of lower concentration. what is this flow of water called? a) active transport b) allocation c) diffusion d) osmosis