关于细胞中化合物的叙述，正确的是（ ）
如图1所示的电路．滑动变阻器最大阻值为R0=58Ω，电源路端电压U随外电阻R变化的规律如图2所示，图中U=12V的直线为图线的渐近线，试求：
读短文，回答问题。
May: Good morning! Can I help you?
Lucy: Yes. I want some pencils and pens.
May: We have many here. Which one do you like?
Lucy: That red one, please.
May: Here you are.
Lucy: Thank you. How much is it?
May: It's cheap. It's 1 yuan.
