"Heat engines and heat pumps are similar in that they both operate on the principle that heat flows naturally from a hot substance to a colder one and, in the process, can be made to do work. However, there is an importance difference between them."

The answer is below

Explanation:

The difference between a heat engine and a heat pump is that a heat engine is a device that converts Thermal energy into Mechanical Energy while a heat pump is a system that extracts heat from a cold body and delivers it to a hot body.

A Heat Engine generates mechanical energy (work) from the temperature difference between two thermal reservoirs while a  Heat pump extract heat from a low temperature reservoir and delivers the heat energy to a high temperature reservoir.

absorption lines are where light has been absorbed by the atom thus you see a dip in the spectrum whereas.

emission spectra have spikes in the spectra due to atoms releasing photons at those wavelengths.

explanation:

a and b sometimes have a positive value