Answer:
The word that cannot complete the sentence "Necesito _____ a mi amigo" is "bailar". The sentence is in the present tense and it is clear that the subject of the sentence (I) needs to do something to or for their friend. The other words provided (ayudar, preguntar, and visitar) are all verbs that could be used in this context, but "bailar" (to dance) does not make sense in this sentence. Therefore, "bailar" is the word that cannot complete the sentence.