The correct answer is D. the Geats' carrying of Beowulf's battle gear from the lake to Herot .
A cannot be a testament to their valor because they abandoned the hero and left him to fight the monster alone. B and C are also wrong because the monster did these, and not the hero. Therefore, the correct answer is D.
While Beowulf was fighting, the Geats carried his battle gear from the lake back to the castle for him to take when he comes back.