I’m not sure but I think it’s b.
For indicating time, the best answer is C- During, because this word tells a reader when an action is taking place.
Again implies that something has been done before, and is being done again, but does not imply <em>when</em> it is being re-done.
Furthermore is a word with a similar meaning to "Also", so it is not connected to the idea of time.
Besides generally means "other than" which, again, has no connection to time.
I think the answer is c. Sentence 3
Sorry if wrong
B would be correct, it is the most definite answer, without any lies/gimmicks.