The correct answer is option 'A', which states that the first treatment Sadao gave to the wounded soldier was washing his wounds. Let's delve into the details of this answer.

Explanation:
When Sadao, a Japanese doctor, found the wounded American soldier on the beach, he immediately decided to provide him with medical aid. As a doctor, Sadao's first instinct was to address the soldier's wounds. Hence, he began the treatment by washing his wounds.

Washing the wounds is an essential step in wound care as it helps to remove dirt, debris, and any foreign substances that may be present. This is important to prevent infection and promote healing. By cleaning the wounds, Sadao aimed to eliminate any potential sources of infection and create a cleaner environment for the wound healing process to commence.

Significance of washing wounds:
1. Prevention of infection: Cleaning the wounds helps to remove bacteria, dirt, and other contaminants that can cause infection. It is crucial to minimize the risk of infection, as untreated infections can lead to severe complications.

2. Promotion of healing: By washing the wounds, Sadao aimed to create a clean and sterile environment that is conducive to healing. Clean wounds are more likely to heal properly and without complications.

3. Removal of debris: In some cases, wounds may contain foreign objects or debris that can hinder the healing process. Washing the wounds can help dislodge and remove such debris, allowing the wound to heal more effectively.

4. Pain relief: Cleaning the wounds can also provide some pain relief. Irrigation with a sterile solution can help soothe the injured area and alleviate discomfort.

Conclusion:
The first treatment Sadao provided to the wounded soldier was washing his wounds. This initial step aimed to prevent infection, promote healing, remove debris, and provide pain relief. By cleaning the wounds, Sadao demonstrated his commitment to providing immediate care to the injured soldier, setting the foundation for further treatment and recovery.