In order to determine which noun "la" substitutes in the sentence, we need to look at the nouns listed:
A. el refresco (the soda) - masculine B. el té (the tea) - masculine C. la leche (the milk) - feminine D. las fresas (the strawberries) - feminine plural
The word "la" is a feminine singular article, which means it could substitute for a feminine singular noun. Therefore, "la" would substitute for:
C. la leche
If the sentence contained "la" as a reference, it would most likely refer to "la leche".