根据短文内容，选择正确答案。
Hello, friends!
    My name is Zhou Dan. I'm a Chinese girl. I'm twelve. I'm from Zhengzhou, China. Do you know Zhengzhou? It's in the middle of China. I'm in No. 8 Middle School. There are about 900 students and 50 teachers in our school. It is a good school in Zhengzhou: I'm in Class 2 Grade 7. There are 49 students in our class: 29 girls and 20 boys. My English teacher is Miss Zhao Dan. Our names are almost the same, right? She is nice to me. We're good friends. I like English, and I like music, too. I want to find a pen-friend. Please write to me.
                                                              Yours,
                                                            Zhou Dan

已知函f（x）= $\{\begin{array}{c}{\log }_{3}x,x>0\\ 2^x,x\le 0\end{array}$ ，则f（f（ $\frac{1}{9}$ ））=____

下列说法正确的是（   ）

以下有关生物遗传与变异的叙述，正确的是（    ）

徽州古民居中建筑规模最大、雕刻艺术威就最高的一座古建筑是