Answer:
C. Protein
Explanation:
Proteins contain C, H, O, and N.
Most notably, they contain an R group (aka a side chain), which is different for each for amino acid. The R group is symbolized by the letter R in the image.
chemical formula??! do you mean O2
Answer: The cell membrane is selectively permeable.
Explanation: going thru last year notes
air water food - good luck