Question

how have humans changed the atmosphere of the planet in the past 200 years?

a. they have increased the levels of greenhouse gases.

b. they have reduced the levels of carbon dioxide.

c. they have reduced the levels of greenhouse gases.

d. they have increased the levels of nitrogen.

Explanation:

In the past 200 years, human activities like burning fossil fuels (coal, oil, gas), deforestation, and industrial processes have released large amounts of greenhouse gases (e.g., carbon dioxide, methane) into the atmosphere. Option B is wrong as human activities increase CO₂. Option C is wrong as greenhouse gas levels have risen. Option D: Nitrogen is mostly from natural processes, and human activities don't significantly increase atmospheric nitrogen levels compared to greenhouse gases. So A is correct.

Answer:

A. They have increased the levels of greenhouse gases.