Aheat engine is a device that uses to produce useful work.

Heat engine is a device which is used to convert the heat energy into useful work

Heat engine extracts heat from high temperature reservoir and then convert that extracted heat into useful work

this process efficiency is calculated by the formula

here we know that

= temperature of high temperature reservoir

= temperature of low temperature reservoir

so now from this we can say that high efficiency heat engine will convert more work

so here correct answer will be

HEAT

probably not if net force is zero

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.