Which statement best describes how greenhouse gases act as natural insulators in the earth's system? a) the gases absorb and emit a part of the heat reflected by earth’s surface. b) the gases receive the sun’s heat directly and deflect a part of it toward earth’s surface. c) the gases are formed by the burning of fossil fuels, as a result of which they are very hot. d) the gases react with each other in the presence of sunlight and release energy in the form of heat.