What does "fit into" mean?

[Javier]

Synonym Search, Intermediate level

ESL/EFL Test #107 "Synonyms for fit and adapt", question 2

Joan moved to Australia more than a year ago but she can't ......... into that new world yet.

(a) suit
(b) fit
(c) accept
(d) harmonize

Synonym Search, Intermediate level

ESL/EFL Test #107 "Synonyms for fit and adapt", answer 2

Joan moved to Australia more than a year ago but she can't fit into that new world yet.

Correct answer: (b) fit
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I guess is ... fit into. I'm not sure? possibly it's a phrasal verb. thanks for the explanation in advanced.

Javier

[Mister Micawber]

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Yes, 'fit into' (= adapt to)-- the other choices do not collocate with 'into'.
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Native English teacher at Mister Micawber's