A heliograph is a semaphore device used for sending optical communications—usually in the form of Morse code—by reflecting flashes of...
GMAT Information and Ideas : (Ideas) Questions
A heliograph is a semaphore device used for sending optical communications—usually in the form of Morse code—by reflecting flashes of sunlight off a mirror. Heliographs were used for rapid communication across expansive distances for military, surveying, and forestry purposes during the late nineteenth and early twentieth centuries, but they were largely effective only during the daytime, and the range of the device depended on factors such as the opacity of the air and line of sight. Therefore, heliographs were eventually replaced by technology that ______
Which choice most logically completes the text?
Step 1: Decode and Map the Passage
Create Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| "A heliograph is a semaphore device used for sending optical communications—usually in the form of Morse code—by reflecting flashes of sunlight off a mirror." |
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| "Heliographs were used for rapid communication across expansive distances for military, surveying, and forestry purposes during the late nineteenth and early twentieth centuries," |
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| "but they were largely effective only during the daytime, and the range of the device depended on factors such as the opacity of the air and line of sight." |
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| "Therefore, heliographs were eventually replaced by technology that ______" |
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Provide Passage Architecture & Core Elements
Main Point: Heliographs were useful communication devices but had environmental limitations that led to their replacement by better technology.
Argument Flow: The passage first defines heliographs and explains their historical uses, then identifies their key environmental constraints (daytime dependency and range limitations), leading to the logical conclusion that they were replaced by technology that overcame these specific problems.
Step 2: Interpret the Question Precisely
This is a fill-in-the-blank question asking us to choose the best logical connector. The answer must create the right relationship between what comes before and after the blank.
Step 3: Prethink the Answer
- The passage clearly establishes that heliographs had specific environmental limitations: they only worked during daytime and their range depended on air opacity and line of sight
- The word "therefore" tells us the replacement technology logically addressed these problems
- The right answer should describe technology that wasn't constrained by these same environmental factors—something that could work in various conditions, not just clear daytime weather with good visibility
- Claims the replacement worked on "similar principles" but was easier to produce/maintain
- This doesn't address the environmental constraints that the passage identifies as the core problem
- States the replacement technology "was not so constrained by environmental circumstances"
- Directly addresses the passage's emphasis on environmental limitations (daytime only, air opacity, line of sight)
- Perfectly matches the logical flow
- Suggests the issue was limited applications (only military, surveying, forestry use)
- The passage presents these as the heliograph's successful uses, not as limitations
- Focuses on eliminating the need for Morse code knowledge
- The passage doesn't suggest Morse code was a limitation or barrier