Final answer:
Gabriel asks about the identity of the seventeen-year-old boy who died for Gretta, reflecting his curiosity and potential feelings of insecurity.
Step-by-step explanation:
Gabriel asks 'What was he?' when he hears that a seventeen-year-old boy died for Gretta years ago. This question reflects Gabriel's curiosity about the boy's identity and possibly his own sense of insecurity or inadequacy. He wants to know more about the boy and understand his significance in Gretta's past.