The correct answer is option 2: Copper. Copper is considered to be the first metal used by humans because it has been found in archaeological sites dating back thousands of years. Copper has excellent properties for early civilizations, such as its ability to be easily shaped and its good conductivity for heat and electricity. This made it ideal for tools, weapons, and decorative items. Copper was also one of the first metals to be smelted and crafted into various useful objects. While other metals like aluminum, iron, and silver were used later in human history, copper was the first metal used by early humans.