C: characters in a novel ideally act and react in a realistic world. true or false

For characters in a novel to be relatable, they have to act realistically to their environments (at least within the boundary of their own character traits)

You have to note that this question is not about stories having to take place in a world similar to ours. Of course, hpothetical concepts are what make stories interesting and that constriction would do fiction an injustice.

What the question really just means that the world reacts normally, that is to say, if it's a hot summer day, it won't just start snowing. (unless the story has good reason for it) Another thing is that you want to prevent "deus ex machina" plot devices (solutions to problems coming out of nowhere) because they remove believability from the world and create a disappointing anticlimax.

true