Garbage collector Jose Gutierrez is 53 years old. When he was young his family was too poor to keep him in school. Jose left school when he was in Grade Two, but that did not stop him having a love for reading.

    Jose said he got the love of reading from his mother. “She read me stories every night,” said Jose. He hopes that every poor child in his city can have books to read. Jose started saving books from garbage twenty years ago. Every day he drives the garbage truck through the city's rich neighborhoods to get old books. Now there are about 20,000 books in Jose's small house. It is already a famous library.

    Books are rare things for children in poor neighborhoods. New books are too expensive. There are nineteen libraries in Bogota, the city where Jose lives, but they are all far from poor neighborhoods.

    Now Jose is famous in Bogota. Many people give old books to him. Jose plans to make more libraries to help more children.

根据短文内容，选择最佳答案。

①民族融合的作用

②分裂中孕育的统一因素

③江南经济的发展

④君主专制逐步加强

已知向量$\overrightarrow{a},\overrightarrow{b}$满足$\left|\overrightarrow{a}\right|=3,\left|\overrightarrow{b}\right|=2\sqrt{3}$，且$\overrightarrow{a}\perp (\overrightarrow{a}+\overrightarrow{b})$，则$\overrightarrow{b}$在$\overrightarrow{a}$方向上的投影为（   ）

据统计，今年无锡鼋头渚“樱花节”活动期间入园赏樱人数约803万人次，用科学记数法可表示为____ 人次．