In science, hardness refers to the measure of how easily a material can be scratched or indented. Given your choices, we can conclude that a material that is not easily scratched is HARD.
Elastic is definitely out of the question because it refers to how much you can stretch a material without it breaking. Toughness refers to how much energy a material can absorb without deforming or cracking. When you refer to strength of material, you measure how much load you can apply on it without it deforming or breaking.
