______________ is the most effective way to control the number of times a user sees an ad.

Q)  ______________ is the most effective way to control the number of times a user sees an ad.
  A)  Setting a lower cost-per-view (CPV) bid at the campaign-level
  B)  Monitoring audience retention metrics with YouTube Analytics
  C)  Setting a frequency cap
  D)  Lowering bidding levels