* Affirmative Tu Command: This means the command is directed to "you" (informal) and is a positive instruction.
* Double Object Pronouns: The sentence uses two object pronouns: "me" (indirect object) and "la" (direct object).
* Combining Pronouns: In Spanish, when using double object pronouns in affirmative tu commands, they are combined into a single pronoun. The order is indirect object + direct object. So, "me la" becomes "mela."
Let's look at the other options:
* A. Me la compras: This is a conjugated verb in the present tense, not a command.
* C. Comprasela: This is incorrect because the pronouns are combined in the wrong order.
* D. Se compras?: This is a question, not a command.
Therefore, B. Compramela is the only sentence that meets all the criteria: it is an affirmative tu command, uses double object pronouns, and combines them correctly.