Why do people live in africa have dark skin?

How did dynasties end and how did new ones start?

A“carpetbagger” would have been most likely to come from which state?

Which of the following  bestillustrates a negative reinforcer?               a.  copland gives up candy to stave off chronic acid indigestion.    b.  nancy learns that she prefers chocolate over vanilla.    c.  carmine changes his major to english lit after failing a math exam.    d.  on a hot day, lindberg always drinks lemonade.