What must be done to coal before it can be used as fuel? It must be made to stick together.
It must be compressed into a very dense substance.
It must be ground into powder.
It must have flammable material added to it.

It must be ground into powder.

Explanation:

"Coal" is one of the nonrenewable resources that humans use for fuel. In order to produce energy, it needs to be burned first. However, efficient combustion happens when the coal is pulverized into fine powder first. This allows the coal to mixed with hot air sufficiently in order to release heat. This then allows the "generation of electricity" that is often used for cooking, lighting, cooling, transportation, healthcare, etc.