Final answer:
Water vapor (H2O) and carbon dioxide (CO2) are the greenhouse gases among the options given. Oxygen (O2) and nitrogen (N2) are not considered significant greenhouse gases as they do not trap heat effectively.
Step-by-step explanation:
Greenhouse gases are gases that absorb and emit radiant energy within the thermal infrared range, which is key to the greenhouse effect. Of the gases listed in the original question—A) O2, B) H2O, C) CO2, D) N2—H2O (water vapor) and CO2 (carbon dioxide) are greenhouse gases. In contrast, O2 (oxygen) and N2 (nitrogen) are not typically classified as greenhouse gases since they do not significantly trap heat in the Earth's atmosphere. Activities such as agricultural production, the burning of fossil fuels, and large-scale deforestation have increased the concentrations of greenhouse gases like CO2, methane (CH4), nitrous oxide (N2O), and other gases, intensifying the greenhouse effect and contributing to global warming.
Water vapor is the most abundant greenhouse gas, responsible for about 80 percent of the natural greenhouse effect. However, it is the increase in CO2 due to human activities that is of significant concern. Methane and nitrous oxide also have a higher global warming potential than CO2, making them notably potent greenhouse gases despite their lower concentrations in the atmosphere.