I think it's C. if we're talking about a rover.
But if it's a rocket that's computerized and automatic (synonym of unmanned)... Then it's B.
The correct answer would be cells
I think the correct answer is option D. The specific heat capacities of similar substances differ because of differences in forces between molecules. Specific heat is the amount of heat absorb or released by a substance to change the temperature to one degree Celsius. Every substance have different structures thus they also have different ways of storing energy and ways to break the bonds they have.