Which of the following statements best describes the carbon atoms present in grass-eating cows?
a. the carbon atoms came from the soil and were incorporated into sugars in the grass.
b. inorganic carbon atoms in the grass were incorporated into organic molecules by the cow.
c. the carbon atoms came from the cow’s mother, which were synthesized from atp.
d. the carbon atoms came from carbon dioxide and were incorporated into sugars through photosynthesis in the grass.

d. The carbon atoms came from carbon dioxide and were incorporated into sugars through photosynthesis in the grass.

Explanation:

Grass eating cows are heterotrophs and can not synthesize the organic sugars by themselves. They derive it from grasses they eat.  

Grasses are the autotrophs that can fix atmospheric carbon dioxide into glucose in the presence of sunlight by the process of photosynthesis. The extra glucose formed during photosynthesis is stored in the cells of grasses in the form of starch and becomes a source of carbon for herbivores such as cows.