**Explanation:**

When the man keeps silent for a moment while gathering salt, the correct answer is option 'D' - he will think of the harm the salt is doing to his hands. Let's break down the reasons behind this answer:

**1. Context of gathering salt:**
- The question states that the man is "gathering salt," which implies that he is physically involved in the process of collecting salt.
- This context is important to understand the impact of silence on the man's actions and thoughts.

**2. Silence and introspection:**
- When the man keeps silent for a moment, it indicates a pause in his actions and possibly his thoughts.
- Silence often creates an opportunity for introspection and self-reflection.
- This moment of silence allows the man to think about the situation and evaluate his actions.

**3. Awareness of harm to hands:**
- The question suggests that the man will think about the harm the salt is doing to his hands.
- Gathering salt may involve exposure to rough and abrasive surfaces, which can cause irritation or damage to the skin.
- By keeping silent and reflecting, the man becomes aware of the physical impact of his actions on his hands.

**4. Contemplation of consequences:**
- During this moment of silence, the man may think about the consequences of his actions.
- He might consider the potential long-term effects of exposing his hands to salt or the immediate discomfort caused by the salt.
- This contemplation allows him to assess whether the benefits of gathering salt outweigh the harm it does to his hands.

**5. Decision-making and future actions:**
- By thinking about the harm the salt is doing to his hands, the man may reassess his approach to gathering salt.
- He might decide to take precautions such as wearing gloves or finding alternative methods to minimize the harm to his hands.
- This thought process and decision-making are crucial for his future actions and well-being.

In summary, when the man keeps silent for a moment while gathering salt, he will think about the harm the salt is doing to his hands. This moment of introspection allows him to become aware of the physical impact of his actions, contemplate the consequences, and make informed decisions about his future actions.