Use the following paragraph to answer Questions 1 and 2.
Many gases make up Earth’s atmosphere, including nitrogen, oxygen, water vapor, argon, methane, and carbon dioxide. Carbon dioxide, water vapor, and methane have the ability to act like an insulator for the planet. Like the windows in a greenhouse, these greenhouse gases trap energy from the sun as heat in our atmosphere. Without their role in this greenhouse effect, Earth would be quite cold. Because of greenhouse gases, the surface of our planet averages around 59°F, making it the perfect place for life. Since about 1850, however, human activities have been releasing extra greenhouse gases into the air, particularly methane and carbon dioxide. Extra methane enters the atmosphere from livestock. Extra carbon dioxide enters the atmosphere by burning fossil fuels such as gasoline and coal for transportation and electricity production. Scientists think that this increase in greenhouse gases has slowly caused a rise in average temperatures across the Earth. Many scientists agree that the greenhouse gas contributing the most to the rise in average temperature is carbon dioxide.
1. What are greenhouse gases?
*
a. gases that are only present in the atmosphere due to human activity
b. gases occurring in buildings where plants are grown
c. gases that act likes insulators for the planet
d. gases that do not occur naturally on Earth