Final answer:
Gabriel's reaction to Gretta's story shows he is attentive and caring, as he listens intently and responds with empathy.
Step-by-step explanation:
In the text, Gabriel's reaction to Gretta's story reveals that he is attentive and caring. His behaviors and actions demonstrate a depth of emotion and a caring nature, as opposed to being talkative, emotionally distant, or angry. He listens intently, asks questions to understand more, and his responses are filled with empathy and support for Gretta. This close attention to Gretta's emotional state indicates that Gabriel is connected and responsive to her feelings, which suggests that the best answer to the provided question would be c) He's attentive and caring.