Prove:

∵EA⊥AD,FB⊥AD，

∴EA‖FB

∴∠E=∠BGC (two straight lines are parallel and have the same angle) ①

∫∠E =∠F② Once again.

①+②

∴∠F=∠BGC

∴CE‖DF (same angle, two parallel straight lines)

Proof of receipt.