Which do you prefer to use to keep in touch with your friends, QQ       WeChat?

已知方程组$\left\{\begin{array}{c}2x+y=4\\ x+2y=5\end{array}\right.$，则x+y的值为 ____．

如图，在平面直角坐标系xOy中，直线y=﹣2x+a与y轴交于点C （0，6），与x轴交于点B．

阅读下面短文，将短文中画线部分的句子翻译成中文
                                                                                How Much Water Is Needed a Day?
   Many people think they should drink eight glasses of water a day．Why? Because that is what they have been told all their life．But a new report on science gives some different suggestions：people should drink according to their bodies．____ They should drink as much water as they would like to drink．
   The report says most people meet their daily needs for water by letting thirst be their guide．It also gives people some good suggestions：women should get about 2.7 liters（升）of water every day，while men should get about 3.7 liters．
   There is an important difference．____ The report doesn’t tell people how many glasses of water to drink．Instead，the experts say it may not be possible to know how many glasses people really need．This is because the daily want of water can include the water in foods．