Pick a molecule
Line-angle drawing
Drawn from the 3D model: the carbon chain lies in the page, Ha and Hb are the pair under test, solid wedge toward you, hashed away. Any other group on a stereocenter is drawn the same way.
The replacement test
Replace one hydrogen of the pair with deuterium, then the other. Compare the two products: identical → homotopic; enantiomers → enantiotopic; diastereomers → diastereotopic.
Verdict
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C H D O
Click atoms to measure.