设函数$f\left(x\right)=\left(2a-1\right)x+b$是$R$上的减函数，则有(     )

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      Jean is a young girl who comes from a rich and famous family. She goes to a good university and has almost everything that money can buy. The problem is that Jean’s family are so busy that they can hardly find time to be with her. Jean is quite lonely (孤独的). So she spends a lot of time on her QQ. She likes being anonymous (匿名的), talking to people who do not know about her famous family and her rich life. She uses the name Linda on QQ and has made a lot of friends.
      Last year Jean made a very special friend on QQ. His name was David and he lived in San Francisco. David was full of stories and jokes. He and Jean had the same interest in rock music and modern dance. So it always took them hours to talk happily on QQ and sometimes they even forgot their time. Of course, they wanted to know more about each other. David sent a picture of himself. He was a tall, good-looking young man with big, happy smile. As time went by, they became good friends and often sent cards and small things to each other.
      When Jean's father told her that he was going on a business trip to San Francisco, she asked him to let her go with him. She wanted to give David a surprise for his birthday. She would take him the latest DVD of a rock singer. But when she knocked on David’s door in San Francisco, she found that her special friend was a 70–year-old man named Jim! How disappointed Jean was!

图示“观察小鱼尾鳍内血液的流动”实验及显微镜下观察到的物像，以下哪项解释合理（　　）

已知双曲线方程$C$:$\frac{x^2}{a^2}-\frac{y^2}{b^2}=1$$\left(b>a>0\right)$的离心率为$e_1$，其实轴与虚轴的四个顶点和椭圆G的四个顶点重合，椭圆G的离心率为$e_2$，一定有（    ）