The correct answer is option 4, Vitamin D. When the human body is exposed to early morning sunlight, it stimulates the production of Vitamin D in the skin. Vitamin D is essential for bone health as it helps in the absorption of calcium and phosphorus, which are important for bone growth and strength. Sunlight is a natural source of Vitamin D and is the most effective way for our bodies to produce it. However, it is important to note that excessive sun exposure can be harmful and increase the risk of skin cancer. It is recommended to spend a limited amount of time in the sun without sunscreen to obtain the necessary Vitamin D, and to protect the skin by wearing protective clothing and using sunscreen when staying in the sun for longer periods.