在极坐标方程中，曲线C的方程是ρ=4sinθ，过点（4，$\frac{\mathrm{\pi }}{6}$）作曲线C的切线，则切线长为（　　）

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。

    I'm a middle school student from America. I live far away from my school. So I often go to school by bus. It takes me about twenty minutes from my home to school.

    But at my school and other schools in our town, there is a "Walk to School Day". It is on Wednesday every week. On that day, parents send their kids to a bus stop. There are many bus stops in our town. At each bus stop, two adults lead us to walk to school together.

    "Walk to School Day" stops us taking cars or buses. That is good for the air and we can get exercise too. On the way to school, we talk to each other. We can also make new friends. I like "Walk to School Day". I walk about five kilometers with other students on that day. Our school will give some students beautiful backpacks if they do well. And I got one last year.

在《大河报》举行的高考状元学习座谈会上，几位高考状元强调，一个人成功与否，主要在于有没有学会学习和学会做人。学会学习就是要求我们做学习的管理者。对于初中生来说，做学习的管理者，应注意（  ）
①学会自主学习   ②提高学习效率    ③科学安排时间   ④经常加班加点    ⑤减轻课业负担