<h2>
1. Re-writing.</h2>
In this exercise, we have the following sentence:
<em>Compré el jabón en la farmacia</em>
That means <em>I bought the soap at the pharmacy, </em>so this sentence is given in the preterite, but this is not we are going to focused on, but in direct object pronoun, which is a pronoun that replaces a direct object (a noun that directly receives the action of a verb). In this case, the verb is comprar conjugated as compré in the preterite. The direct object is el jabón, so the corresponding direct object pronoun is lo, because it stands for the third person singular, then the sentence can be rewritten as:
<em>Lo compré en la farmacia</em>
<h2>
2. Answer the question.</h2>
In this exercise, we need to answer a question replacing the direct object by the corresponding direct object pronoun. The question is:
<em>¿Compraste los patines?</em>
Here we are using the verb comprar conjugated as compraste that matches the second person singular (informal form). On the other hand, the direct object is los patines that matches the third person plural (masculine form). So we replace this direct object by the direct object pronoun that also matches this person, which is los. Therefore, an affirmative answer is:
<em>Sí, los compré</em>
Since I am the one who bought the roller skates (patines), then we use the conjugation of the verb comprar for the first person singular, which is compré.