The citizens of a town are aware of climate change, and they want to make changes to control it. One change they consider is replacing the nearby thermal power plant with a hydroelectric plant. If they want to make sure this change will help to slow climate change, which question should they ask?

How hydroelectric plant is better over thermal power plant in creating less pollution?

Explanation:

The thermal power plant utilizes the coal as a fuel. The heat energy so produce after burning coal is used for generating electrical energy. The burning of the coal results in the production of pollutants. The carbon dioxide is also a chief pollutant of coal burning. This can pollute the air.

The hydroelectric plant is better than thermal power plant in the sense no fuel is required for this purpose the energy from water currents are used for generating electrical energy.  

So, the citizens should research about hydroelectric plant and try to know how it is efficient in providing routine energy supply and impact it exerts on the environment if used as a source of energy generation.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

he would use the colour black