Actin is present in thin filament

Answer

### Step-by-Step Solution:

1. **Understanding Actin**:
- Actin is an intracellular protein found in all eukaryotic cells. It plays a crucial role in various cellular functions, including muscle contraction and cell movement.

2. **Composition of Thin Filaments**:
- Thin filaments are primarily composed of actin. They consist of two helically arranged filamentous polymers of the actin protein.

3. **Additional Proteins in Thin Filaments**:
- In addition to actin, thin filaments also contain another protein called tropomyosin. Tropomyosin runs along the length of the actin filaments and is involved in regulating muscle contraction.

4. **Role of Troponin**:
- Along with actin and tropomyosin, thin filaments also have a globular protein called troponin. Troponin is found at intervals along the filament and plays a key role in muscle contraction by interacting with calcium ions.

5. **Conclusion**:
- Therefore, it is accurate to state that actin is present in thin filaments, as it is one of the main components that make up these structures in muscle cells.