Which best describes why Iowa Jima was significant in US attempts to reach Japan

The reason Iwo Jima was such a significant victory for Allied Forces in the Pacific was that the island had a dense population of Japanese Soldiers, underground bunkers, tunnels, and traps throughout the island. The US wanted Iwo Jima, so they could use the island as a base for Aviation, and ground troops. It was the ultimate reason we were able to drop bombs on Hiroshima and Nagasaki ultimately causing Japan to surrender.