A:①③
B:①④
C:②③
D:②④
寺 辰 恐 笼 庐
kǒng____ sì____
lú____ chén____ lǒng____
如图,已知长方形ABCD的周长为20,AB=4,点E在BC上,AE⊥EF,AE=EF,求CF的长.