Final answer:
The giant boulder blocking the cave entrance prevented Odysseus and his men from escaping.
Step-by-step explanation:
The correct answer to the question is B) A giant boulder blocking the cave entrance. After Odysseus and his men blinded the Cyclops and managed to escape from the cave, they found that a giant boulder had been rolled in front of the cave entrance, preventing their escape. They were trapped inside until Odysseus devised a plan to make the Cyclops move the boulder and enable their escape.