Known: as shown in the figure, ad ∥ BC, ab ∥ DC, verification: △ ABC ≌ △ CDA

It is proved that: ∵ ad ∥ BC, ∵ ab ∥ DC, ∵ ab ∥ DC, ∵ ab ∥ 1 = ∥ 4, in △ ABC and △ CDA, ∥ 1 = ∥ 4ac = Ca ∥ 3 = ∥ 2, ∥ ABC ≌ △ CDA (ASA)

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