Which of the following are true with reference to taxonomical aids?
a. Separate taxonomic keys are requried for each taxonomic category.
b. Herbarium is a store house of collected plant and animal specimens.
c. Each statement in the key is called couplet.
d. Keys are used for identification purpose.

Options

A. a and b
B. a and d
C. a and c
D. c and d

Answer

To determine which statements about taxonomical aids are true, let's analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement A: Separate taxonomic keys are required for each taxonomic category.**
- Taxonomic keys are tools used to identify organisms based on their characteristics. Different taxonomic categories (like species, genus, family, etc.) have distinct characteristics that require separate keys for accurate identification.
- **Conclusion:** This statement is **true**.

2. **Statement B: Herbarium is a storehouse of collected plant and animal specimens.**
- A herbarium is specifically a collection of preserved plant specimens. It does not include animal specimens; those are usually stored in zoological collections or museums.
- **Conclusion:** This statement is **false**.

3. **Statement C: Each statement in the key is called a couplet.**
- In taxonomic keys, each individual statement that provides a choice for identification is referred to as a "lead." A "couplet" refers to a pair of contrasting statements that guide the user in making a choice between two options.
- **Conclusion:** This statement is **false**.

4. **Statement D: Keys are used for identification purpose.**
- Taxonomic keys are indeed used for the identification of organisms. They help in distinguishing between different species based on their characteristics.
- **Conclusion:** This statement is **true**.

### Final Answer:
The true statements regarding taxonomical aids are **A and D**.