This question is based on the following paragraph. The sentences are numbered to help you answer the question. (1) Scientists generally agree that Earth is getting warmer due to what's called the greenhouse effect. (2) A greenhouse stays warm because sunlight and heat coming through the glass roof are mostly trapped. (3) The heat doesn't radiate back into the atmosphere because it's held in by the glass. (4) Something like that happens on Earth. (5) The atmosphere acts like a blanket that keeps the Sun's heat from leaking away into space.

What is the main conclusion you are to draw from this paragraph?

A. Greenhouses help most to grow more quickly.
B. The atmosphere is what keeps the planet warm.
C. The sun's heat can easily leak away out into space.
D. The greenhouse effect is changing Earth's atmosphere.