题目

若向量||=，||=2，（﹣）⊥，则、的夹角是（ ） A．   B．  C． D． 答案：D【考点】平面向量数量积的运算． 【分析】利用数量积的定义、向量垂直与数量积的关系即可得出． 【解答】解：∵向量||=，||=2，（﹣）⊥，设向量与的夹角是θ． ∴=﹣=2﹣2cosθ=0， ∴cosθ=． ∵θ∈[0，π]，∴θ=． 故选：D．— How many passengers were in the plane?— It ________ 100,20 Japanese ________. [     ]A. contained; included  B. contained; includingC. included; contained  D. contained; containing