△ABC的外接圆的圆心为O，半径为1，2$\overrightarrow{OA}$+$\overrightarrow{AB}$+$\overrightarrow{AC}$=$\overrightarrow{0}$且$\overrightarrow{OA}$=$\overrightarrow{AB}$，则向量$\overrightarrow{BA}$在向量$\overrightarrow{BC}$方向上的投影为（　　）

某兴趣小组为了测定某未知碘片中碘化钾的含量，进行了如图实验：

（查阅资料知：碘化钾易溶于水，而碘化银是不溶于水的黄色沉淀）

阅读课文5～7段，回答问题。

阅读下面短文，从短文后所给的A、B、C、D四个选项中选出能填入相应空白处的最佳选项。

    This is an apple tree. There are many 1 on the tree. There are some 2under it, too. They are 3 happily. Under the tree I can 4 a boy and a girl. They're playing games with the dogs.  The boy is 5 a blue sweater and white shoes. He is Jim. He is 6 American student. He is 14. He 7 his school very much. The girl is Jim's sister, 8 name is Cindy. She is 11. She is in a yellow dress. Her shoes are yellow. 9 . Now they are standing here, they are waiting for their friends. They 10 to play games under the tree.