该错误是由于在label中列出 Dataframe 系列而不是仅列出列名而引起的;尝试使用：
4. Based on the advanced digital technology, the Nikon Cool Pix 995 camera provides the excellent performance. 5. Let us now examine the case that the mass flow rate of air is smaller than 3 kg/s. 6. Finally, we make a conclusion in section 5. 7. We selected the method to solve ...