It is Saturday. The Browns are at home. Mrs. Brown is in the kitchen. She is making lunch. Mr. Brown isn't in the living room. He is outside. He is washing his car. The car is new and very beautiful. Jim is playing football with some boys. Where is his sister, Sue? She's watching TV in her bedroom with her friend, Ann.

已知D为△ABC的边BC的中点，△ABC所在平面内有一个点P，满足 $\overrightarrow{PA}$=$\overrightarrow{PB}$+$\overrightarrow{PC}$，则 $\frac{\left|\overrightarrow{PD}\right|}{\left|\overrightarrow{AD}\right|}$的值为（　　）

如图是制作人体口腔上皮细胞临时玻片标本的过程，其正确顺序为（　　）

—Are the beaches in Dalian beautiful?

—Sure. They___________ lots of tourists from home and abroad every year.