Final answer:
The correct pronoun to use is 'le' to say 'Juan likes the food.'
Step-by-step explanation:
The correct pronoun to fill in the blank is le. The sentence should be: A Juan le gusta la comida.
In Spanish, when referring to a person's likes or preferences, we use the pronoun 'le' followed by the verb 'gusta'. This construction is called the 'leísmo' and it is commonly used in some regions, including parts of Spain and Latin America.
For example, if Juan likes pizza, we would say: A Juan le gusta la pizza.
Learn more about Subject Pronouns in Spanish