Proteins are biomolecules composed of `alpha-` amino acids. An `alpha-`amino acid has a general formula `R-underset(underset(NH_(2))(|))(C)-COOH`. The amino acids polymerise and form an amide linkage (peptide linkage) between two monomeric amino acid units. The polymerisation takes place as follows `H_(2)N-overset(overset(R_(1))(|))(CH)-underset(underset(O)(||))(C)-OH+H- underset(darr underset((-2H_(2)O))("Polymerisation"))(HN-overset(overset(R_(2))(|))(CH)-underset(underset(O)(||))(C))-OH+H-NH- overset(overset(R_(3))(|))(CH)-underset(underset(O)(||))(C)-OH` Two or more similar amino acids can also polymerise, for example a dimer will be like. `H_(2)N- overset(overset(R)(||))(CH)-underset(underset(O)(||))(C)-NH-overset(overset(R)(||))(CH)-underset(underset(O)(||))(C)-OH`. In the above trimer, if `R_(1)=H , R_(2)=CH_(3)` & `R_(3)=Ph` then total number of optically active stereoisomers will be :A. 8B. 6C. 4D. 2