The monomer of following polymer is
`[-O-underset(CH_3)underset(|)CH-CH_2-COO-underset(C_2H_5)underset(|)CH-CH_2-CO-]_n`
A. `HO-CH_2-CH_2-COOH`
B. `HO-underset(CH_3)underset(|)CH-CH_2-COOH`
C. `HO-underset(C_2H_5)underset(|)CH-CH_2-COOH`
D. both b and c