Agening is slow or absent in

Options

A. Plants
B. Parrot
C. Hydra
D. Unicells

Answer

### Step-by-Step Solution

1. **Understanding Aging**: Aging refers to the process of becoming older, which is often associated with a decline in biological functions and an increase in the likelihood of death.

2. **Identifying the Options**: The options given are:
- A. Plants
- B. Parrot
- C. Hydra
- D. Unicellular organisms

3. **Analyzing Each Option**:
- **A. Plants**: Plants are multicellular organisms and they do exhibit aging, although some may have long lifespans.
- **B. Parrot**: Parrots are also multicellular organisms and they age, showing signs of aging as they grow older.
- **C. Hydra**: Hydra is a simple multicellular organism known for its regenerative capabilities, but it still ages, albeit slowly.
- **D. Unicellular organisms**: These organisms, such as bacteria and protozoa, can reproduce asexually and may show very slow aging processes. They can undergo spontaneous DNA damage, but their aging is not as pronounced as in multicellular organisms.

4. **Conclusion**: Among the options, unicellular organisms exhibit the slowest aging process. Therefore, the correct answer is **D. Unicellular organisms**.

### Final Answer
**D. Unicellular organisms**