已知Rt△ABC中，∠A=90°，则$\frac{b}{c}$是∠B的（　 　）

阅读理解

    Good morning．Welcome to our school!

    My name is Hou Li，a history teacher.I'm your guide today．Look!Our big playground lies in the middle of the school．On the left of it are two black classroom buildings．There are thirty classrooms in each building．We use computers to help with teaching．It's quick and saves much time．We also put important information on the Internet．so our students can read it at home．Of course,they do their homework on the computers too，just like your students in America．We're going to join an IT lesson at nine o'clock there．

    On the right are three buildings：the office building,the dining hall and the library．The dining hall is orange．Six hundred students can eat in it at a time．Today we are going to have lunch there．The library is a popular place．There are many kinds of magazines and newspapers and hundreds of books for students and teachers．

    Let's have a rest near the office building and then go to the IT lesson．

根据材料内容选择最佳答案。

设f(x)为定义在R上的奇函数，当$x\ge 0$时，$f\left(x\right)=2^x+2x+b$（b为常数），则f(-1)=（   ）