6.2.1 Complete the sentences with the correct forms of the prepositions and articles
d) the unstressed personal pronouns o, a, os, as with the prepositions a, de, em, por (ao, à, às, do, das, no, pelo etc.)
At the moment it is perhaps still unclear which preposition is to be used. Hear first the sentence and complete then the sentence with the correct combination of preposition and pronoun. You get the acento grave you need for the crase, when the preposition a collides with the articles a / as, by pressing the shift key and the accent key and then the a.