The organic molecules in living organisms have a measurably lower ratio of carbon-13/carbon-12,two stable isotopes of carbon that comprise approximately 1.1% and 98.9% of atmospheric carbon,respectively.What is a reasonable explanation for this phenomenon?

A)Photosynthesis preferentially uses carbon dioxide molecules with carbon-12, and the lower carbon-13/carbon-12 ratio propagates through the food chain.
B)Carbon dioxide molecules with carbon-13 stay in the upper atmosphere and are less available to terrestrial plants and algae.
C)Carbon-13 has a different valence electron configuration and is therefore less chemically reactive than carbon-12.
D)Oxygen atoms preferentially react with carbon-13, thereby enriching the atmosphere with carbon dioxide molecules containing carbon-13 atoms.
E)Carbon dioxide molecules containing carbon-13 are heavier and sink into the ocean depths, making them less available to living organisms.