question: steel chain bridge:steel
choices.label: A B C D
choices.text: stone tower:bricks bun:flour erhu:strings Internet:optical fiber
explanation: one of the main raw materials of a "chain bridge" is "steel", and the "chain bridge" can be made of "steel". the main raw material of the "stone tower" is stone, not "brick". "flour" is not a property of "buns. wood is one of the main raw materials of "erhu", and "string" is the component of "erhu", not the raw material of "erhu" the "internet" is not a physical object, "optical fiber" is used as an information transmission medium to provide "internet" access services, and the raw material of the "internet" is not "optical fiber"
relation: steel chain bridge steel R3.7
relation: bun flour R3.7
relation: erhu strings R2.3