(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. Glass ceilings are important to greenhouses.
B. The greenhouse effect is changing Earth's atmosphere
C. Greenhouses help most plants to grow more quickly
D. The sun's heat can easily leak away out into space