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People's Education Edition, Grade Two, Answers to Math Book Exercises, 103, 13 questions, how to do it quickly and urgently, and rewards.
Because ABCD is a square.

So AB=CD=AD=BC

∠A=∠B=∠C=∠D=90

Because AE=BF=CM=DN.

So BE=BF=CM=AN

So △ AEN △ BFE △ CMN △ DENM

EF=FE=MF=NF

EFMN is a diamond.

△AEN?△BFE

∠AEN=∠BFE

Because ∠BFE+∠BEF=90

∠AEN+∠BEF=90

Then ∠NEF=90

The diamond EFMN is square.