题目

Last summer vacation, I volunteered to work at a vet’s（兽医诊所）. There I saw a lot of dogs. Minnie was the funniest-looking dog I’d ever seen. Short thin curly hair covered her sausage-shaped（香肠形）body. Her eyes always seemed surprised. And her tail looked like a rat’s tail.She was brought to the vet because her owners didn’t want her any more. I thought Minnie had a sweet personality, though. “No one should judge her by her looks,”I thought. Finally, I advertised Minnie in the local paper. “Funny-looking dog, well-behaved, needs a loving family.”When a boy ca已知菱形ABCD边长为2，∠BAD=120°，点E，F分别在边BC，DC上，BE=λBC，CF=λCD，若AE•BF=-1，则λ= ．