The second law of thermodynamics states that
when a process converts energy from one form to another, some energy converts into heat, an unusable form of energy
energy can neither be created nor destroyed, but it can change from one form to another
energy flows through ecosystems without being recycled most energy in ecosystems comes from the sun

The correct answer is  (a) when a process converts energy from one form to another, some energy converts into heat, an unusable form of energy.

This means that the 100% energy produced is not converted into the 100% work done some part of that energy is loss in the form of heat.  Example: If a car runs with fuel, engine will only stop once the fuel is over. The car will not run until the fuel is refilled into it. Some of the the energy is released in the form of heat once the car is refilled.

that is wrong, its not thymus.