Three of these four are alike in one way. Choose the odd one out: Bronze, Brass, Copper, Steel.

Bronze, brass and steel are alloys, each made by melting two substances together — bronze from copper and tin, brass from copper and zinc, steel from iron and carbon. Copper stands alone as a pure metal, a single element dug out of the earth. It sits comfortably with the rest because it is the very metal two of those alloys are built from, but the group is held together by being mixtures.