Answer: 
This investment served the purpose of a medium of exchange and store of value. 
Explanation: 
Tara used $50,000 from her investment in certificates of deposit as a down payment to buy a house. 
Since this investment stored value for future use, it performed the function of a store of value. 
The investment then was used to make a down payment for a house, so it performed the function of a medium of exchange.