which of the following describes a compound? (Hint: Carbon and Oxygen both appear on the periodic table.)

A. a piece of pure carbon, containing only carbon atoms.

B. oxygen gas surrounding a solid piece of carbon.

C. a substance made of two oxygen atoms for each carbon atom.

D. Carbon and Oxygen atoms mixed without being bonded together.

PLEASE HELP ME ASAP WKSNSNSNXSNDSNDSJ