题目

He tried to join the Army but to his disappointment ended up being ____________ because of poor health and eyesight. A. turned down       B. turned back       C. turned over        D. turned against 答案：A 解析: 略设=4，若在方向上的投影为2，且方向上的投影为1，则的夹角等于（ ）A．B．C．D．