What expression does the boy use to show sympathy towards the girl being ill?

The expression "Sorry to hear" is commonly used to convey sympathy and compassion towards someone who is experiencing a difficult situation, such as illness. This phrase acknowledges the other person's struggle and expresses empathy, showing that the speaker cares about their feelings. It indicates a level of emotional understanding and concern, making it an appropriate response when someone shares bad news about their health.

In contrast, the other choices lack the same level of emotional resonance or suitability for expressing sympathy. "Sad to know" is somewhat valid but doesn't carry the same weight of empathy; "Disappointed to listen" might imply a negative judgment rather than concern, and "Upset to hear" can suggest that the speaker is more affected by the news than the person who is ill. These alternatives do not convey the same direct expression of sympathy that "Sorry to hear" achieves.