In quadrilateral ABCD, ad ∥ BC, in order to judge whether quadrilateral ABCD is parallelogram, it should also satisfy () A.∠A+∠C=180° B.∠B+∠D=180° C.∠A+∠B=180° D.∠A+∠D=180°

D.∠A+∠D=180°
That is: AB / / DC

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