1. https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.Series.html
2. https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.html
3. https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.drop.html
4. https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.loc.html