The word 'acquiring' in the context of language means gaining or learning it. Option 2 appears to repeat the word itself due to a typographical issue in the paper; it was most likely intended to read 'learning (a language)', which is the accurate meaning of 'acquiring'.
Note: Option 2 reproduces the keyword 'acquiring' itself, which appears to be a printing issue in the NTA paper. We have picked option 2 as it is the only choice that matches the intended meaning of 'gaining/learning a language'.