已知点M在平面ABC内，并且对空间任一点O，$\overrightarrow{OM}$=x$\overrightarrow{OA}$+$\frac{1}{2}$$\overrightarrow{OB}$+$\frac{1}{3}$$\overrightarrow{OC}$则x的值为（　　）

肾脏的结构和功能的基本单位是（  ）

一个细胞进行3次分裂，形成几个细胞？（  ）

Kitty is a lovely girl. Today she goes to the city to visit her aunt. There are so many hotels and restaurants in the city. She can't find the way to her aunt's house. She is lost. She wants to cross(穿过)the street. But there are too many buses and cars. She feels afraid. She stops in the middle(中间). A policeman comes and helps her to cross the street. Then he tells(告诉) Kitty how to get to her aunt's house. Kitty says“thank you”and then she gets there safely(安全地). Both(两者都) Kitty and her aunt are happy.

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—It's about ten minutes' walk.