Which of the sentences below is an affirmative tu command that uses double object pronouns and corresponds to the following sentence A. Me la compras B. Compramela C. Comprasela D. Se la compras?

Only answers B & C are tú commands as opposed to A & D which are present-tense usage of verbs in the tú conjugation. Cómpramela, means "buy it for me", whereas "Cómprasela", means "buy it for him/her/it". You will have to judge which is proper by context.