What do "that" and "it"in the following sentence refer to ?
Schoolwork is almost everything, so we study hard and that's it.
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Sign up to join this communityI would say "... and that's it" is a shortened form of "...and that's all there is to it." The phrase is somewhat idiomatic.
That would refer to the notion that "schoolwork is almost everything." The sentence could be rephrased as, "Schoolwork is almost everything, so we study hard and there is nothing more to say about the matter." It's a way of expressing how we are resigned to the truth about something.