Correct answer:
entre
Entre is a preposition that means between and is not followed by de. So the other preposition is al lado de that is a preposition that can be translated as beside, next to. Recall that a preposition is a word (or group of words) which is used to show the way which other words are connected, that is, they are used to indicate a relationship between two words or phrases, between nouns, between nouns and verbs, and between different parts of a sentence. We often use them to indicate relationships of location, direction, or time.
