I'm assuming that the choices are the ways urban landfills use to increase decay rate for most trash? If so, then the answer would be '<span>increase the number of aerobic bacteria'. Increasing the number of aerobic bacteria increase the decay rate for most trash.</span>
I think the best answer is D.
The more sunlight there is, the warmer the water gets. The warmer water is, the less dissolved oxygen the water contains. The cooler water is, the more dissolved oxygen it contains. Some sunlight is still needed, as water that is too cool will form ice.