Which of the following are the most abundant elements in the living cells?AC, H, S and PBC, O, N and PCC, H, O and NDC, H, Mg and Ca

The most common elements in living things are carbon, hydrogen, oxygen, nitrogen. 
A carbohydrate is a biological molecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms.
Proteins are made up of amino acids which are organic compounds  (C, H, and O) containing amine (-NH2), along with a side chain (R group) specific to each amino acid.
Each nucleotide consists of a nitrogen-containing aromatic base attached to a pentose sugar (C, H, and O), which is in turn attached to a phosphate group.