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.

Which sentence is the paragraph's topic sentence?

A. Sentence 3
B. Sentence 1
C. Sentence 2
D. Sentence 5

Answer 1

Answer: B

Sentence 1 is the paragraph's main topic. It works to introduce what the greenhouse effect is and it's there to establish that this is what scientists generally think causes the Earth to get progressively warmer.

A (sentence 3) cant be the main topic because this sentence is merely a detail of how the greenhouse effect works. Option D is not the answer because this is just additional information of how the greenhouse effect works on earth. Finally, option C (sentence 2) is not because it does not introduce the greenhouse effect, it only expands on the first sentence.