How do managed placements on the Display Network work?

17) How do managed placements on the Display Network work?

  A)  Advertisers can guarantee placement on prominent and popular sites.
  B)  Advertisers manually select the desired sites on which their ads may appear
  C)  Keywords are used to place ads next to content that matches the ad.

  D)  Appropriate sites are automatically chosen for the advertiser by the Google AdWords system.