Answer:
C. It is warmer than Cube B.
Step-by-step explanation:
Option C would be correct because energy as heat flows from warmer objects to cooler objects. If heat flows from Cube A to Cube B, then Cube A must be warmer than Cube B.
Reasoning behind the other option being incorrect:
D: This is incorrect because the direction of heat flow does not depend on the relative size of the cube.
A: This is incorrect because energy as heat would flow from Cube B to Cube A if Cube A is cooler than Cube B.
B: This is incorrect because the direction of heat flow does not depend on the relative sizes of the cubes also.