Step 1: Definition
Condensation polymers are formed by the combination of monomers with the elimination of small molecules like water, methyl alcohol, etc.
Step 2: Analysis
- Rubber, PVC, and polyethene are addition polymers.
- Proteins are natural polymers formed by the condensation of $\alpha$-amino acids.
Step 3: Conclusion
During the formation of proteins, amino acids link together via peptide bonds ($-CONH-$) with the release of water molecules.
Final Answer: (b)