Why should you avoid adding duplicate keywords across ad groups?

59) Why should you avoid adding duplicate keywords across ad groups?

  A)  Identical keywords will compete against each other, and because both ads may serve - it may increase your CPCs
  B)  None of these options are correct
  C)  Identical keywords are not allowed in AdWords and your ads will be disapproved

  D)  Identical keywords compete against each other, and the better-performing keyword triggers your ad.