Exam-style question
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Which observation supports the conclusion that the Universe is expanding?.
- A.The cosmic microwave background radiation is uniform.
- B.Galaxies exhibit a redshift that increases with distance.
- C.The abundance of light elements matches Big Bang nucleosynthesis.
- D.The rotation curves of galaxies imply dark matter.
Model answer
What a good answer should say
- Galaxies exhibit a redshift that increases with distance.
Explanation
Why this works
A systematic increase of redshift with distance is the empirical basis of Hubble's law and indicates an expanding Universe.
Common mistake
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