Which is the best example of the function of money called "unit of account"?

A. A bar of gold will still have value in 10 years, though it might be worth more or less than it is today.

B. 10 carrots can buy 1 cantaloupe today or 1 cantaloupe in 2 weeks.

C. 10 beads can buy Jamie a screwdriver from Larry. Larry can use those beads to buy a bag.

D. A dollar bill can buy 1 chocolate bar