Choose the correct statement:

Options

A. Sun can be taken as an inexhaustible source of energy
B. There is infinite storage of fossil fuel inside the earth
C. Hydro and wind energy plants are non-polluting sources of energy
D. Waste from a nuclear power plant can be easily disposed off

Explanation

To solve the question, we need to analyze the statements provided and determine which one is correct based on our understanding of Huygens' principle.

### Step-by-Step Solution:

1. **Understanding Huygens' Principle**:
- Huygens' principle states that every point on a wavefront can be considered a source of secondary wavelets. The new wavefront is formed by the tangential surface to these wavelets.

2. **Analyzing the Options**:
- **Option A**: "Huygens' principle is valid only for transverse waves."
- This statement is incorrect because Huygens' principle applies to both transverse and longitudinal waves, not just transverse.

- **Option B**: "Huygens' principle is valid only for longitudinal waves."
- This statement is also incorrect for the same reason as option A; Huygens' principle is valid for both types of waves.

- **Option C**: "Huygens' principle is valid for both transverse and longitudinal waves."
- This statement is correct. Huygens' principle applies to both types of waves.

- **Option D**: "The shape of the wavefront on Earth for sunlight is cylindrical."
- This statement is misleading. While light can be considered to have cylindrical wavefronts at close distances, by the time sunlight reaches Earth, it is effectively treated as a plane wavefront due to the vast distance from the Sun.

3. **Conclusion**:
- The correct statement among the options is **Option C**: "Huygens' principle is valid for both transverse and longitudinal waves."