Final answer:
The sentence that best shows the problem Parvana's family is trying to solve is the one about needing someone to go to the market to buy food and supplies, as it directly impacts their survival.
Step-by-step explanation:
The problem that Parvana's family is trying to solve is most likely related to the survival and functioning of the household in difficult circumstances. In this context, the sentence that best shows the problem the family is trying to solve is b) Someone has to go to the market to buy food and supplies. This sentence highlights a direct issue affecting the family’s ability to sustain themselves and indicates a clear necessity that must be addressed.