题目

Peter’s jacket looked just the same as Jack’s，but it cost________his. A．as much twice as B.twice as much as C．much as twice as D.as twice much as 答案：B定义：|×|=||•||•sin θ，其中θ为向量与的夹角，若||=2，||=5，•=-6，则|×|等于    ．