Answer:
c. "...Sorrow/Had returned to Denmark. They'd traded deaths..."
Step-by-step explanation:
This is the sentence that best describes the aftermath of Grendel's mother's attack upon the Danes. In this sentence we learn that sorrow had returned to Denmark. This means that the Danes were mourning something. We also learn that they "traded deaths." Therefore, this indicates that the mourning of the Danes was due to the deaths inflicted by Grendel's mother in her attack.