已知$\overrightarrow{a}$,$\overrightarrow{b}$是平面向量，若$\overrightarrow{a}$$\perp$($\overrightarrow{a}$-2$\overrightarrow{b}$)，$\overrightarrow{b}$$\perp$($\overrightarrow{b}$-2$\overrightarrow{a}$)，则$\overrightarrow{a}$与$\overrightarrow{b}$的夹角是（  ）

中国人口分布很有特色，东部多西部少，大致有一条东北－西南走向的分界线，此线是（      ）

如图所示为演示交变电流的装置图，关于这个实验，正确的说法是(  )

    I have many favorite hobbies．I like____magazines and books．My parents like dancing．On Sunday in the morning they go to the park to do morning____．In the park they sing and dance but I am reading a____ book．On Sunday afternoon I am going to the bookshop to read____books．It is fun．Sometimes I play table tennis with grandparents．I also like taking____，too．They are interesting．