The answer to the question is option 'C', which states that 40% of our body weight is due to muscles.

Muscles play a crucial role in our body's structure, movement, and overall functioning. They are responsible for all types of movements, from simple tasks like walking and talking to complex actions like playing sports or lifting heavy objects. Let's explore why muscles contribute significantly to our body weight.

1. Function of Muscles:
- Muscles are responsible for generating force and producing movement in our body.
- They help in maintaining body posture and stability.
- Muscles enable us to perform voluntary actions and control our body movements.

2. Types of Muscles:
- There are three types of muscles in our body: skeletal muscles, smooth muscles, and cardiac muscles.
- Skeletal muscles are attached to our bones and are responsible for voluntary movements.
- Smooth muscles are found in the walls of our internal organs, such as the stomach and intestines, and control involuntary movements.
- Cardiac muscles are specific to the heart and enable it to beat and pump blood throughout the body.

3. Muscle Mass and Weight:
- Muscles are dense and contain a significant amount of protein, which contributes to their weight.
- Skeletal muscles, being the largest type of muscle, play a major role in determining our body weight.
- Skeletal muscles are attached to our bones, providing support and structure to our body.
- The more muscle mass we have, the higher our body weight will be.

4. Body Composition:
- Body weight is composed of various components, including bones, muscles, organs, tissues, and fluids.
- While bones also contribute to body weight, they account for a smaller percentage compared to muscles.
- On average, muscles make up about 40% of our body weight, whereas bones account for approximately 15%.

5. Importance of Muscle Health:
- Maintaining strong and healthy muscles is essential for overall well-being.
- Regular exercise and physical activity help in building and maintaining muscle mass.
- Strong muscles support good posture, joint stability, and overall body strength.
- Muscles also play a role in metabolism, as they burn calories even at rest.

In conclusion, the correct answer is option 'C' - muscles. Muscles contribute significantly to our body weight due to their density, protein content, and role in movement, stability, and body composition.

On an average, probably 40% of body weight is because of muscles.