Biologists Label Various Carbohydrates,fats and Amino Acids with Radio-Isotopes,place Them

Biologists label various carbohydrates,fats and amino acids with radio-isotopes,place them in a cell culture,and allow time for cell metabolism.Then by disrupting cells in a blender and separating out various cell organelles,they find the radioactive molecules can be detected as part of various cellular compounds although visible cell structures appear unchanged.Therefore

A) these "food" molecules are used only for energy.
B) most cell components are constantly being broken down and rebuilt.
C) molecules diffuse at random through the cytoplasm and into cell organelles.
D) radioactivity has an unusual role in metabolism of living cells.