That's that vs. that's it?

[Thunu]

English Language Tests, Intermediate level

ESL/EFL Test #208 "What Comes Next? (2)", question 10

We can safely say that the business is now concluded so ..........

(a) that's him
(b) that's us
(c) that's it
(d) that's them

English Language Tests, Intermediate level

ESL/EFL Test #208 "What Comes Next? (2)", answer 10

We can safely say that the business is now concluded so that's it.

Correct answer: (c) that's it
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That's it is the same as "that's that".

Am I right?

Thu
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Reach an agreement as ploughing, don't let argument happen at crops.

[Mister Micawber]

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Yes, that's about right.
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Native English teacher at Mister Micawber's