The correct answer to the question is B. Hair growth.
1. **Digestion**: Muscles are involved in the process of digestion. For example, the smooth muscles in the digestive system help move food along the digestive tract through a process called peristalsis.
2. **Blood temperature**: Muscles play a significant role in regulating body temperature. When the body temperature rises, muscles can produce heat by increasing their metabolic activity. This helps in maintaining a stable body temperature.
3. **Speech**: Muscles, particularly those in the face, mouth, and throat, are essential for speech production. Muscles in the vocal cords, tongue, and lips work together to create different sounds and articulate words.
4. **Hair growth**: Hair growth is not directly affected by muscles. Hair growth is primarily influenced by factors like genetics, hormones, and overall health rather than muscle activity.
In conclusion, while muscles play a crucial role in many bodily functions such as digestion, regulating body temperature, and speech, they do not have a direct impact on the process of hair growth.
