如图所示，L为理想变压器，其原线圈、副线圈的匝数分别为n₁ n₂ ④为理想交流电流表，阻值分别为R、r的两个定值电阻接在电路中．将a、b两端接到电压恒定的交流电源上，当开关S分别拨至接线柱l和2时，发现电流表的示数相同．则两个定值电阻的阻值之比r/R等于(   )  

阅读短文，选择正确的答案。
    My school is very big and very beautiful. You can see some beautiful grass and flowers in the garden. In summer, we can fly kites and play sports on the playground. There is a big library in my school. In the library, you can read many interesting books. I like it very much.
I love my school very much. Welcome to my school.

下列关于超重与失重的说法中，正确的是（　　）

已知 $a=2^{2.1}，b={(\frac{1}{2})}^{-\frac{1}{2}}，c=lo{g}_5$ 4，则a，b，c的大小关系为（   ）

阅读诗词《竹石》，回答

《竹石》是一首什么诗？