Source: Official Guide Revised GRE 1st Ed. Part 4; Set 6; #4


It can be inferred that the greenhouse roof

It can be inferred that the greenhouse roof is designed to allow for which of the following? For hot desert locations with access to seawater, a new greenhouse design generates freshwater and cool air. Oriented to the prevailing wind, the front wall of perforated cardboard, moistened and cooled by a trickle of seawater pumped in, cools and moistens hot air blowing in. This cool, humidified air accelerates plant growth; little water 5 evaporates from leaves. Though greenhouses normally capture the heat of sunlight, a double-layered roof, the inner layer coated to reflect infrared light outward, allows visible sunlight in but traps solar heat between the two layers. This heated air, drawn down from the roof, then mixes with the greenhouse air as it reaches a second sea-water-moistened cardboard wall at the back of the greenhouse. There the air absorbs 10 more moisture, which then condenses on a metal wall cooled by seawater, and thus distilled water for irrigating the plants collects. The avoidance of intense solar heat inside the greenhouse, The entry of sunlight into the greenhouse to make the plants grow, The mixture of heated air with greenhouse air to enhance the collection of moisture

2 Explanations


Prashant Jha

Hey Chris, for the option B there is no mention in the passage of the entry of sunlight into the greenhouse to make the plants grow. To make plants grow??? should we assume that?? is that not an outside information again???

Jul 17, 2016 • Comment

Cydney Seigerman, Magoosh Tutor

Hi Prashant,

I would say that we can consider common knowledge the fact that plants need light to grow. So, we can say that the entry of sunlight will help/make plants in the greenhouse grow :)

Does that make sense?

Jul 24, 2016 • Reply

Hugo Zhang

Hi, Cydney! I have the same question with Prashant. You said that we could use common knowledge to choose answer choice B. However, I think that the strategy when doing GRE like reading comprehension question is the "idiot principle", which means we can only use the information based on what the passage mentions. I remember Chris mentions this in his introduction video lessons. And I've also read the passage at least 3 times and didn't find any information about answer choice B). So why could we choose B as one of the correct answer? How can we solve this paradox?

Sep 9, 2016 • Reply

Sam Kinsman, Magoosh Tutor

Hi Hugo,

You're right that we shouldn't use outside information on the GRE! However, as Cydney mentioned, it's OK to use basic, common knowledge. That is, we can use information that every test taker can reasonably be expected to know. The fact that sunlight makes plants grow is common knowledge, so we can use that for this question!

I hope that helps :)

Sep 15, 2016 • Reply

Diogo Cosin

Hi, Sam,

Don't you think that to use common knowledge holds a dangerous precedent, given that what is common knowledge for one may not be for another person? Soon, how exactly define common knowledge can be a hard task once the test taker should be able to decide one fact as common or not during the test.

Sep 25, 2017 • Reply


Hi Diogo,

The GRE definitely expects you to bring certain aspects of knowledge to bear on the exam. Knowing that sunlight is involved in the growth of plants is certainly something that the GRE may expect you to know and use on the test, as this question written by the same people who write the actual GRE illustrates.

Sep 28, 2017 • Reply


Gravatar Chris Lele, Magoosh Tutor

Oct 6, 2012 • Comment

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