Category is

Options

A. (a) a rank in hierarchy
B. (b) any grouping of living objects
C. (c) a term used interchangeable with taxon
D. (d) a taxonomic grouping

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the correct definition of "category" in the context of biological classification.

2. **Defining Category**: In biological classification, a "category" refers to a rank within the taxonomic hierarchy. This hierarchy is a system used to classify and organize living organisms based on shared characteristics.

3. **Taxonomic Hierarchy**: The taxonomic hierarchy consists of several ranks, typically including:
- Kingdom (highest rank)
- Phylum
- Class
- Order
- Family
- Genus
- Species (lowest rank)

4. **Importance of Taxonomic Hierarchy**: The classification helps in understanding the diversity of life and aids in the identification and classification of unknown organisms. It was developed by Carl Linnaeus in the 18th century.

5. **Evaluating Options**: The question likely provides multiple-choice answers. We need to evaluate each option:
- **Option A**: "A rank in hierarchy" - This aligns with our definition of category.
- **Option B**: "Any grouping of living objects" - Too broad and not specific to taxonomy.
- **Option C**: "A term used interchangeably with taxon" - Incorrect, as "category" and "taxon" are not the same.
- **Option D**: "A taxonomic grouping" - While related, it does not specifically define "category."

6. **Conclusion**: Based on the evaluation, the most appropriate answer is **Option A: "A rank in hierarchy."**