The answer you are looking for is C. Visitó.
When you conjugate a verb, you change the ending based off of who you're talking about, and the ending of the original verb. Here are the conjugations based on their endings (please note this doesn't account for all verbs, such as Ser, or Tener).
- I (Yo): Add an "o" to the end.
- You (Tú): Add "as" for "AR" verbs, or "es" for "ER" and "IR" verbs.
- He, she, you, it (Él, ella, usted): Add "a" for "AR" verbs or "e" for "ER" and "IR" verbs.
- We (nosotros): Add "amos" for "AR" verbs, "emos" for "ER" verbs, and "imos" for "IR" verbs.
- They, you all (Ellos, ellas, ustedes): Add "an" for "AR" verbs, and "en" for "ER" and "IR" verbs.
Since "visitar" is an -AR verb, and you are looking for the Yo (I) form, the conjugation would be visitó.
I hope this helps!