You are writing an essay on whether nuclear power or coal-burning plants cause more pollution for the environment, and you need concrete facts.

which is a concrete fact you could use in your essay and not an abstract assertion?

a) the debate over which pollutes the environment more--nuclear power or coal-burning--rages on in the scientific community.
b) coal burning plants and nuclear power plants are both important because they employ many people who need those jobs to support their families.
c) some people are afraid of nuclear power because it produces nuclear waste and yet ignore the plumes of smoke polluting the air in the coal factory two miles away.
d) the fact that nuclear power plants have more federal regulations placed upon them than coal-burning power plants show that nuclear plants are far safer and cleaner.