Why was it difficult for american forces to defend themselves against japanese fire?

During the invasion of Iwo Jima, approximately 70,000 American troops arrived to the island. However, a force of around 20,000 Japanese soldiers had entrenched themselves in the mountains. Moreover, these soldiers had built tunnels throughout the island. Therefore, when American troops arrived, they encountered very strong resistance from the Japanese. It made it very difficult for Americans to protect themselves against Japanese fire.

gaius cassius longinus and marcus junius brutus, former enemies of julius caesar who'd joined the roman senate, led caesar's assassination, dubbing themselves "the liberators." and the second one is   the assassination of julius caesar was the result of a conspiracy by many roman senators led by gaius cassius longinus, decimus junius brutus albinus, and marcus junius brutus. they stabbed caesar (23 times) to death in a location adjacent to the theatre of pompey on the ides of march 15 march 44 bc.

i thinl it is the 1st answer