Correct Response: D. Aquatic dead zones are regions of water in which the dissolved oxygen content is so low that it cannot support life. Warmer water holds less oxygen, and discharge from nuclear power plants can contribute to the formation of dead zones by raising the temperature of the local water systems. Increased levels of acidity (A) and decreased light penetration (C) are conditions created by dead zones, rather than causes. Background radiation (B) is the natural radiation that occurs in the environment, so any increased radiation in the region surrounding a nuclear power plant would not be considered background radiation.
