矩形ABCD中，E、F分别是AD、BC的中点，CE、AF分别交BD于G、H两点．

求证：

设$\overrightarrow{a}$=(1,1,-2)，$\overrightarrow{b}$=(x,y,z)若x²+y²+z²=16，则$\overrightarrow{a}$$·$$\overrightarrow{b}$的最大值为____ 

用简便方法计算．

$\frac{2}{5}\times 80+\frac{3}{5}\times 80$

    I like sports very much. Last weak, I took part in the school basketball match. It was so____（令人愉快的).The fans____ (为...加油 )us on and we played____(好的) than usual so we won the match. Our teacher was very____(满意的)with us and we took photosinthe____(体育馆)。

    Doing sports is a good____(选 择 )to keep fit. There are____大 量 )of sports for us to choose. Some of my ____( 同学)like playing volleyball and others like playing baseball .For me, basketball is my favourite.

    Let's do sports now. It makes us have more____(机会) of making fiends. What's more, the more you do sports, the____(健康的) you will be.