Hint: The greenhouse effect is a natural process which warms the surface of the earth. Common examples of greenhouse gases include carbon dioxide, methane, water vapor, nitrous oxide, ozone and chlorofluorocarbons. The energy that is absorbed warms the surface and atmosphere of the Earth.
Complete answer: When the environment becomes enriched with nutrients, it leads to eutrophication. It is a problem in marine habitats like lakes because it causes algal blooms. Some of the algae produce toxins which are harmful to the higher forms of life. This will lead to problems in the food chain and it affects animals which feed on them. The ozone layer is present in the stratosphere and it is also called the ozonosphere. The ozone which is present in the lower atmosphere i.e. in the troposphere is a pollutant and is very harmful. It is known as bad ozone. But the ozone found in the stratosphere is beneficial to life on planet earth because it protects the planet from harmful ultraviolet rays and other radiations. So, it is also known as good ozone.
Therefore, option B is the correct answer.
Eutrophication is mainly caused by human activities because of their excess use of nitrate and phosphate fertilizers. The nutrients in these fertilizers accumulate in the water bodies and help in the overgrowth of algae. When algae starts to grow, it blocks sunlight from entering into the water and it uses up the oxygen.