∵BD是∠BAC的平分线,DE⊥AB,∠C=90°,
易得△BCD≌△BED,
∴CD=DE,BE=BC,
∴△ADE的周长=DE+AE+AD,
=CD+AD+AE,
=AC+AE,
=BC+AE,
=BE+EA,
=AB,
=10cm.
故选C.