What's the greenhouse effect?

A. The release of extra moisture from water vapor

B. Human-caused global warming

C. The regulation of atmospheric and surface temperatures

D. The trapping of warm air in cities

B. Human-caused global warming

Explanation:

The greenhouse effect is when the energy form the sun comes to the earth and doesn't reflect to space, so the energy stays as warm air and changes the climate of the planet doing the weather everytime more hot.