The best piece of evidence Thalia could use to support Reason 3, which states that another parking lot would just increase traffic downtown, is:
C. Many people ride the bus or walk to shops downtown, but a parking lot would encourage people to drive instead of using these more environmentally friendly methods of transportation.
This evidence directly addresses how adding a parking lot would likely lead to more cars on the road, increasing traffic, which aligns with her argument against creating a parking lot.