16Hit1600
Information and IdeasVery hardInference from a trend without its expected cause

Information and Ideas practice question

Each year the observatory records the number of nights on which its telescope could be used. That number has fallen steadily for two decades, even though rainfall and cloud cover in the region have not changed over the same period. The astronomers suspect that ____

Which choice most logically completes the text?

  1. A. something other than the weather — such as growing light or haze from the nearby city — is cutting into the usable nights.Correct
  2. B. the region's climate has become steadily wetter.
  3. C. the telescope is being used less because fewer astronomers work there.
  4. D. there are fewer stars in the sky than there were two decades ago.

Answer: A. something other than the weather — such as growing light or haze from the nearby city — is cutting into the usable nights.

The obvious cause, weather, is ruled out by the text. What remains is a non-weather cause that has grown over twenty years — a city's light or haze fits.

Why the other answers are wrong

B. the region's climate has become steadily wetter.
The text says rainfall and cloud cover have NOT changed.
C. the telescope is being used less because fewer astronomers work there.
The count is of nights the telescope COULD be used, not nights it was used.
D. there are fewer stars in the sky than there were two decades ago.
Nothing suggests the sky itself has changed.

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