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Information and IdeasVery hardMain idea of a passage about a measurement

Information and Ideas practice question

Early estimates of the glacier's retreat relied on comparing photographs taken from a fixed ridge over sixty years. The method was simple but flattering to the glacier: the ridge overlooked its thickest section, where thinning shows least. Satellite altimetry, which measures surface height across the whole ice body, finds that the glacier has lost nearly twice the volume the photographs implied.

Which choice best states the main idea of the text?

  1. A. The photographic method understated the glacier's loss because of where it looked, and whole-glacier measurements show a much larger decline.Correct
  2. B. Photographs are more accurate than satellites for measuring glaciers.
  3. C. The glacier has not retreated at all.
  4. D. The ridge is the best place to observe the glacier.

Answer: A. The photographic method understated the glacier's loss because of where it looked, and whole-glacier measurements show a much larger decline.

A vantage point that hid thinning; altimetry doubles the estimate.

Why the other answers are wrong

B. Photographs are more accurate than satellites for measuring glaciers.
The opposite.
C. The glacier has not retreated at all.
It has lost volume.
D. The ridge is the best place to observe the glacier.
The ridge overlooked the least revealing section.

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