How would a video recording be useful in understanding a historical event ?
a. it would offer multiple perceptives on an event
b. it would be vetted by experts
c. it would show the way an event appeared without bias
d. it would allow historians to understand how people in the past thought about history

C. it would would show the way an event appeared without bias.

I would say C, "It would show the way an event appeared without bias," because videos (unless they're edited or otherwise altered to reflect the filmmaker's point of view, in which case they're less of a video recording and more of a movie) give us a look at exactly what happened for ourselves as if we were there instead of hearing an account from someone else.

Just to quickly eliminate the others as well...
A is wrong because a video is objective and doesn't offer any perspectives itself, just the truth. B is wrong because while a video might be vetted by experts, that's not something that would make it uniquely useful. All historical sources and artifacts are vetted by experts for authenticity, but that doesn't have any impact on or connection to how useful they are. And even if it did, that wouldn't be something that was specific video, which is what the question is asking. And D is wrong because video recordings cannot show what people are thinking about an event -- they only show the event occurring.