Which of the following choices contains two ways in which carbon enters the atmosphere? A. Erosion and transpiration
B. Volcanic Activity and Photosynthesis
C. Human Activity and Nitrogen-Fixing Bacteria
D. Emissions from Factories and Respiration

d. or c. is what I think I limited your options

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

b tumor cells have a cell wall instead of a membrane

explanation:

tumor cells different from normal cells because tumor cells have a cell wall instead of a membrane.