A its Stratosphere, Sorry I didn't see your answer, its bilogy I think not physics.. :)
I think it's B hope it helps
Answer:
forces that are equal in size and opposite in direction. Balanced forces do not result in any change in motion. unbalanced. forces: forces applied to an object in opposite directions that are not equal in size. Unbalanced forces result in a change in motion.

hope helpful ~
2.5 kg because you cant change the weight of the rock
Convection is the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat