Answer:
He really likes Mary.
Step-by-step explanation:
Pronouns are the words that we use in place of a noun. In other words, pronouns replace nouns that are repeated, used to refer to things or persons talked about, or substitute the nouns in a sentence.
In the given sentence "Ricardo really likes Mary", the subject noun is "Ricardo" while "Mary" is the object noun. To replace the subject noun with a pronoun, we need to use a gender pronoun. And since Ricardo is a male, then the gender pronoun will be "he".
Thus, the correct sentence becomes "He really likes Mary".