给下列句子选出正确的答语。
____①Do you have hens? A. Wow! They're so cute!
____②What are those? B. No, they are goats.
____③How many horses do you have? C. Yes, we do.
____④Look! These are cows. D. They're hens.
____⑤Are those sheep? E. Twelve.
若向量 a→ =(1,1), b→ =(2,﹣1), c→ =(﹣1,2),则 c→ 等于( )