In which TrueView format(s) can an advertiser use a companion banner?

A) In-stream and in-display
B) All of the listed answers are incorrect
C) In-stream
D) In-display

The correct answer is:

C) In-stream

Explanation: A clickable thumbnail image that accompanies a TrueView in-stream ad. On a YouTube page, it appears next to the ad, in the top right corner (on a desktop computer).

 

Read more here: https://support.google.com/partners/answer/6293542?hl=en