Verbs ending in -ir that undergo stem changes in the present tense also under go stem changes in the preterite. These verbs have a stem change in the second person formal singular (usted), third person singular (él, ella) and third and second person plural (ellos, ellas and ustedes) forms.
The correct answer would be your choice A. Because, "servidor" means: "a server" (referring to a person) while "nariz" = "Nose," "chimenea" = "chimney," "arbol,"= "tree." Hope that helps! :D
