Replace the indirect object with the corresponding pronoun.
Los mapuches venden joyas de lapislázuli a las turistas.
Answer: Los mapuches les venden joyas.
The Mapuches sell them jewelry.
Explanation: The indirect object of the verb "vender" is "las turistas", which is a plural noun and the indirect object pronoun has to agree in number with the noun. Les venden a las/los turistas.
