Answer:
C. A cube that is 1 yard long, 1 yard wide, 1 yard high
Explanation:
A unit cube has a volume of 1 cubic unit.
This means that the length, width, and height are all 1 unit.
Answer choice C is the only one that has a cube with the length, width, and height at 1 unit.
This means it is a unit cube because the volume will be 1 cubic unit.
So, C is the correct answer.