选择合适的单词完成句子。

读问句，选择对应的答句。

____ ①Let's go to the library.                                    A. Yes, I do.

____ ②Where is the teacher's office?                       B. Yes, it is.

____ ③Do you have lunch at school?                         C. Forty-six.

____ ④How many desks are there in your class?        D. OK.

____ ⑤Is that your pencil?                                          E. It's on the first floor.

已知一次函数$f\left(x\right)=kx+b$的图像经过点$P\left(1,2\right)$和$Q\left(-2,-4\right)$，令$a_n=f\left(n\right)f\left(n+1\right),n\in N^{*}$，记数列$\left\{\frac{1}{a_n}\right\}$的前项和为$S_n$，当$S_n=\frac{6}{25}$时，$n$的值等于（   ）

某单位有老年人28人，中年人54人，青年人81人．为了调查他们的身体状况，需从他们中抽取一个容量为36的样本，最适合抽取样本的方法是(　　)