函数$f\left(x\right)=x·\left(\frac{1}{2^x-1}+n\right)$为偶函数，则实数n的值为____ ．

阅读理解

B

      A father sat at his desk thinking of his poor family life when his young son ran in and said happily, “Dad, because this is your birthday and you’re 50 years old, I’m going to give you 50 kisses, one for each year!” But the father said, “Oh, Andrew, don’t do it now. I’m too busy!” Hearing this, the boy said nothing as tears (眼泪) ran down in his big blue eyes. The father felt sorry for his son, and then he said, “You can finish later.”

      The boy walked away, with disappointment on his face. That evening the father said, “Come and finish the kisses now, Andrew!” But the boy didn’t answer.

      Unluckily, a few days later, the boy had an accident (事故) and left his father forever.

      Love is a two-way street. We must warmly accept (接受) any loving act, or we will feel sorry.

在$△ABC$中，a=b是$a\cos A=b\cos B$的  (    )

实验室有一瓶标签残缺的溶液，它可能是硫酸钠、碳酸钠和氯化钠溶液中的一种。龙龙、开开两位同学分别设计了下表方案进行鉴别。