With TrueView in-stream ads, an advertiser pays:

Q)  With TrueView in-stream ads, an advertiser pays:

  A)  only when the viewer clicks the video.
  B)  when the viewer watches at least 30 seconds of the video or completes it.
  C)  when the viewer watches five seconds of the video.
  D)  on a cost-per-thousand-impressions (CPM) basis.