A. The connotation of the word careless suggests that Marta doesn't pay attention to her things.
Explanation:
Careless, as used in the passage, shows that she was not being careful with her glasses thus she ended up breaking them. Since the passage said that she usually broke them within a week, we can infer she isn't careful with any pair of her designer glasses she has bought. Therefore, it cannot be B because she does NOT really care about her things, and C is off-topic because it never says that she prefers designer sunglasses, only that that is what she always bought.