短文改错

    My swimming experience is extreme interesting. There was a time when I swim like a rock.This went on till one day when I was fishing with a friend of mine at nearby pond. I was so much careless that I slipped into one. Had my friend not come to my rescue, I would have be drowned. Ever since then, I have come to know the importance of learn to swim. I didn't go to any training class but  learned it all by me. Now I have no difficult swimming at all . Though the way I swim looks clumsy ,at least it can keep me floating. Thinking of this, I feel quite satisfying.

如图，在矩形ABCD中，AB=5，BC=6，点E，F，G，H分别在已知矩形的四条边上，且四边形EFGH也是矩形，GF=2EF．若设AE=a，AF=b，则a与b满足的关系为（　　）