The answer to your question would be that the word a translator could use to replace the underlined word without changing the meaning of the sentence is the following one: Thrilled. That is, the correct option would be D.
Merriam Webster Dictionary defines "overjoyed" as "filled with great joy". Then, "thrilled" means "extremely happy about something". As you can see, these words can be taken as "synonyms" and therefore they can replace one another.