Final answer:
The word "al" correctly completes the sentence.
Step-by-step explanation:
The correct word to complete the sentence is B. al.
In Spanish, we use the preposition al when we want to express movement towards a specific place, like going to a store. So the sentence would be: Ella quiere ir al supermercado.
Another example would be: Voy al cine (I'm going to the cinema).
Learn more about Spanish prepositions