In $2010,$ Tara used $$50,000\mathrm{.}00$ from funds she had invested in certificates of deposit as a down payment to buy a house. What function did this portion of her investments serve when she made the down payment?

Question $19$ options:

a$)$

medium of exchange.

b$)$

unit of account.

c$)$

store of value.

d$)$

unit of exchange.