The correct choice to fill the blank is 'la meilleure amie' because it means 'the best friend,' which fits the context of a close relationship. The other options do not imply as strong a bond as this phrase does. Therefore, Emilie is described as the best friend of the speaker's sister. ;
The correct option to fill in the blank is 'la meilleure amie,' meaning 'the best friend.' This choice reflects the close relationship described in the sentence. The other options suggest more casual or inappropriate connections.
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