XOM                                                                             Exxon Mobil Corporation
MS                                                                                Morgan Stanley
CVX                                                                           Chevron Corporation
BAC                                                                          Bank of America Corporation
ABBV                                                                     AbbVie Inc
RHHBY                                                                 Roche Holding AG
PFE                                                                       Pfizer Inc
BHP                                                                       BHP Group Limited
CSCO                                                                    Cisco Systems, Inc
SHEL                                                                     Shell plc
Present the graphs of the stock prices of the  portfolios in each subperiod (2018-2019
and 2020-2021). Provide comments on the graphs