Question

Coal _____. is a renewable resource can easily be replenished is formed from plant remains is the least-polluting energy source

Answer 1

Coal . . . . .

-- is a renewable resource that can easily be replenished.
   It happens by itself, and you don't even need to do anything,
   but it takes several million years.

-- Is formed from plant remains, and

-- is perhaps the MOST polluting energy source.

Answer 2

There is only supposed to be one answer choice, so the correct answer is is formed from plant remains.