Questões de Concurso Público Prefeitura de São Borja - RS 2019 para Professor de Português/Inglês

Consider the following changes proposed:
I. Replacement of ‘sheds light on’ (l.07) with ‘clarifies’. II. Replacement of ‘handful’ (l.18) with ‘large number’. III. Replacement of ‘corroborate’ (l.37) with ‘validate’.
Disregarding any grammatical aspects, which ones alter the meaning of the sentence?

Consider the following statements about the text:
I. Linguistic research suggests that accents are strongly shaped by the speaker's first language they learned growing up. II. The work is the first to evaluate these effects on a large scale and may help to improve methods of teaching for adults learning an additional language. III. New research pinpoints how to overcome specific problems related to more than 60 different languages when learning a foreign language.
Which ones are correct?