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.

Which sentence is the paragraph's topic sentence?
A.Sentence 5
B.Sentence 3
C.Sentence 2
D.Sentence 1

Answer is D as the topic is the general subject of a paragraph or essay Title. As you can see the author started listing some examples to support the main idea/topic.
What is the main conclusion you are to draw from this paragraph?
A.The sun's heat can easily leak away out into space.
B.The greenhouse effect is changing Earth's atmosphere.
C.The atmosphere is what keeps the planet warm.
D.Greenhouses help most plants to grow more quickly.

correct answer is B. The greenhouse effect is changing Earth's atmosphere. A is incorrect because the excerpt says that the atmosphere keeps the Sun's heat from leaking away into space. C is incorrect because it is the greenhouse effect that keeps the planet warm. D is not even mentioned in the text, which means that only B is correct.


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