## Core Concept
The question pertains to the structural aspects of proteins, specifically to the types of secondary structures that proteins can form. Alpha helix and Beta pleated sheet are fundamental structures in biochemistry.

## Why the Correct Answer is Right
Alpha helix and Beta pleated sheet are indeed examples of **secondary structures** of proteins. The secondary structure of a protein refers to the local arrangements of a protein's polypeptide chain, primarily through hydrogen bonding. The alpha helix is a spiral structure stabilized by hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another, four residues away. The Beta pleated sheet, on the other hand, consists of beta strands aligned parallel or anti-parallel to each other, also stabilized by hydrogen bonds. These structures are crucial for the overall 3D conformation and function of proteins.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not correspond to the correct categorization of alpha helix and Beta pleated sheet.
- **Option B:** This option is incorrect for the same reason as Option A; it does not accurately represent the structural category of alpha helix and Beta pleated sheet.
- **Option C:** This option might seem plausible but is incorrect because it does not accurately categorize alpha helix and Beta pleated sheet.

## Clinical Pearl / High-Yield Fact
Understanding the secondary structures of proteins, such as alpha helices and beta pleated sheets, is essential for comprehending protein function and the effects of mutations. For example, diseases like Alzheimer's are associated with the formation of beta-amyloid plaques, which are primarily composed of beta pleated sheets.

## Correct Answer: B. Secondary structure.