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E1cB elimination is most likely when the substrate has

  1. Aan acidic beta-hydrogen and a poor leaving group such as
  2. Ba tertiary carbon bearing a good leaving group such as
  3. Cno beta-hydrogen
  4. Da bulky leaving group in a non-polar solvent without base

Answer: A

E1cB needs a beta-H acidic enough (for example alpha to a carbonyl) to be removed by base, giving a stabilised carbanion. Because the carbanion forms first, a poor leaving group such as is acceptable.
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