Final answer:
The sentence where the pronoun comes before the antecedent is 'Her caring made Keiko a good sister.' The pronoun 'Her' refers to Keiko, who is mentioned afterward.
Step-by-step explanation:
In English grammar, a pronoun must agree with its antecedent in number, gender, and person. The antecedent is the word that the pronoun refers to, and it usually appears before the pronoun in a sentence. However, sometimes the pronoun can come before the antecedent, which can cause confusion. In the sentences provided:
Keiko handed her little brother his coat.
He would get very cold without it.
Her caring made Keiko a good sister.
They went out into the snow together.
The sentence in which the pronoun comes before the antecedent is sentence C: "Her caring made Keiko a good sister." The pronoun 'Her' is used before we know that it refers to 'Keiko.' In all the other options, the antecedent either comes first or is present in a previous sentence.