The Spanish language uses the imperfect tense to talk about past actions that were repetitive or in progress at a given moment in the past. There are more uses, though.
Option A is not correct because a completed action in the past would require the perfect tense, not the imperfect.
Option C is also not correct because an action happening right now would require the present tense.
Option D cannot be correct because, among other things, the sentence says "Cuando era pequeña" (When she was a kid) so it is not an action that just happened.
Additionaly, by saying that "[...] hacía travesuras" it does not intend to express that she was naughty one time, rather, it conveys that that behavior repeated itself over time.
No te pido dinero. La vendedora nos muestra muchas chaquetas a Laura y a mí. ¿Quíen pagará sus estudios a Manuel? Nosotros pensamos comprar regalos para (a) nuestras madres.
