题目

 I have two                       .                      A. pencil-box                     B. pencil-boxes                  C. pencil-boxs 答案： B3．在△ABC中，|AB|=5，|AC|=6，若B=2C，则向量$\overrightarrow{BC}$在$\overrightarrow{BA}$上的投影是（　　）A．$-\frac{7}{5}$B．$-\frac{77}{125}$C．$\frac{77}{125}$D．$\frac{7}{5}$