_________ are optional, clickable thumbnail images that appear next to TrueView InStream ads on YouTube.

Q)  _________ are optional, clickable thumbnail images that appear next to TrueView InStream ads on YouTube.
  A)  Companion banners.
  B)  TrueView in-display ads.
  C)  Display ads on the Google Display Network (GDN).
  D)  YouTube mastheads.