Final answer:
The correct pronoun to fill in the blank is 'te'.
Step-by-step explanation:
The correct pronoun to fill in the blank is te. The sentence should be "A ti te gustan las plantas." In this sentence, the pronoun te is used to indicate that the plants are pleasing to you or that you like them. The pronoun te is the second person singular form of the pronoun 'you' in Spanish.
Learn more about Spanish pronouns