Final answer:
The correct answer to the question is b) Sheet, referring to the β-Pleated sheet, which is a secondary structure in proteins stabilized by hydrogen bonds between the backbone's amino and carbonyl groups in antiparallel polypeptide strands.
Step-by-step explanation:
The student's question asks about the secondary structure formed by a 40 residue segment of protein, which folds into a two-strand antiparallel configuration. The correct answer is b) Sheet, specifically a β-Pleated sheet. This secondary structure is characterized by hydrogen bonds forming between the partially positive nitrogen atom in the amino group and the partially negative oxygen atom in the peptide backbone's carbonyl group. In antiparallel β-pleated sheets, the polypeptide strands run in opposite directions, creating a stable structure due to the alignment of hydrogen bonds.