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655-705 (Hard)|   Weaken|                              
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Images from ground-based telescopes are invariably distorted by the 20 Dec 2025, 05:12
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ChiranjeevSingh GMATNinja Nowhere in the passage can one directly infer what exactly large-aperture telescopes are; they are ground-based or orbiting space telescopes, I'm not sure. Reading answer choices (C) and (D) gives me hints, but I'm still unsure. Can that be reasonable grounds to eliminate choices (C) and (D)?
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Images from ground-based telescopes are invariably distorted by the 20 Dec 2025, 14:49
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siddhantvarma
ChiranjeevSingh GMATNinja Nowhere in the passage can one directly infer what exactly large-aperture telescopes are; they are ground-based or orbiting space telescopes, I'm not sure. Reading answer choices (C) and (D) gives me hints, but I'm still unsure. Can that be reasonable grounds to eliminate choices (C) and (D)?
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No, it's not because the facts that they are telescopes that are located where there is "wind," in (C), and that they are are called "Earth-based," in (D), indicate that they are ground-based telescopes.
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Images from ground-based telescopes are invariably distorted by the 21 Dec 2025, 01:22
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For E, how do we know "more light-gathering capacity" could be provided by ground based telescopes? Reading this option, I don't quite get how just because space telescopes are not sufficient, ground based wont be absolete? There could be other telescopes that (beyond ground) that could serve the gap in space telescopes? So how does that weaken the conclusion?
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Images from ground-based telescopes are invariably distorted by the Earth's atmosphere. Orbiting space telescopes, however, operating above Earth's atmosphere, should provide superbly detailed images. Therefore, ground-based telescopes will soon become obsolete for advanced astronomical research purposes.

Which of the following statements, if true, would cast the most doubt on the conclusion drawn above?

(A) An orbiting space telescope due to be launched this year is far behind schedule and over budget, whereas the largest ground-based telescope was both within budget and on schedule.

(B) Ground-based telescopes located on mountain summits are not subject to the kinds of atmospheric distortion which, at low altitudes, make stars appear to twinkle.

(C) By careful choice of observatory location, it is possible for large-aperture telescopes to avoid most of the kind of wind turbulence that can distort image quality.

(D) When large-aperture telescopes are located at high altitudes near the equator, they permit the best Earth-based observations of the center of the Milky Way Galaxy, a prime target of astronomical research.

(E) Detailed spectral analyses, upon which astronomers rely for determining the chemical composition and evolutionary history of stars, require telescopes with more light-gathering capacity than space telescopes can provide.

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Images from ground-based telescopes are invariably distorted by the 21 Dec 2025, 03:39
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siddhantvarma
ChiranjeevSingh GMATNinja Nowhere in the passage can one directly infer what exactly large-aperture telescopes are; they are ground-based or orbiting space telescopes, I'm not sure. Reading answer choices (C) and (D) gives me hints, but I'm still unsure. Can that be reasonable grounds to eliminate choices (C) and (D)?
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Hi siddhantvarma,

To add to MartyMurray's point, the question tells us that orbiting space telescopes operate above Earth's atmosphere, which means they can't be affected by wind (it's safe to assume that there's no wind of the kind we're talking about in space).

The bottom line is that we can't eliminate those options just because they mention "large-aperture telescopes".
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Images from ground-based telescopes are invariably distorted by the 21 Dec 2025, 03:50
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For E, how do we know "more light-gathering capacity" could be provided by ground based telescopes? Reading this option, I don't quite get how just because space telescopes are not sufficient, ground based wont be absolete? There could be other telescopes that (beyond ground) that could serve the gap in space telescopes? So how does that weaken the conclusion?
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Hi soniasw16,

Something that people already rely on needs more light-gathering capacity than space telescopes have, which means those telescopes must be "non-space telescopes". You're fine till here. But you can go one step further and assume that the only remaining option is ground-based telescopes. By "beyond ground" if you're thinking water/underground, that's fine for particle detectors etc., but it's unreasonable for light-gathering telescopes.
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Images from ground-based telescopes are invariably distorted by the 15 Feb 2026, 20:46
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Why that feels convincing

“Best Earth-based observations” sounds exclusive.

But read carefully:

best Earth-based observations

This only compares ground telescopes with other ground telescopes.

It does NOT compare them to space telescopes.

So D means:

👉 Among ground telescopes, these are best.
❌ It does NOT say space telescopes cannot observe the Milky Way center.

GMAT Language Trap
Phrase What it actually limits
best Earth-based only ground telescopes
best observations could still be worse than space

GMAT loves category-restricted superlatives.

🔍 Your Concern 2: “E doesn’t say ground telescopes CAN do it”

This is a sharp observation — let’s examine.

What E says:

Spectral analyses require more light-gathering capacity than space telescopes can provide.

Implication:

Advanced research relies on spectral analysis.

Space telescopes lack needed capacity.

Therefore, another telescope type must provide it.

On GMAT, we assume:

👉 If advanced research is happening today, and space telescopes cannot do it, ground telescopes must.

Otherwise, the research would be impossible.

🧠 Why E Still Works Without Explicitly Naming Ground Telescopes
Weaken answers don’t need to prove the alternative fully.
They only need to show the conclusion is doubtful.
Conclusion: ground telescopes will be obsolete.
E shows:
👉 space telescopes cannot perform essential research.
That alone destroys the certainty of obsolescence.
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Images from ground-based telescopes are invariably distorted by the 12 Apr 2026, 03:42
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D is best "Earth Based" not overall. If one considers "ground-based telescopes will soon become obsolete" the conclusion then your point is definitely valid. But if one considers "Superior feature of space telescope will cause ground-based telescopes to be obsolete", then option E is correct. In GMAT this causal relation as a conclusion is often tested.
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