When you use paper money to pay for food, the money is a
medium of exchange
store of value
unit of account

The correct answer for the fill in the blank is - medium of exchange.

Explanation-

When we use paper money to pay for food, the money is a medium of exchange as  we are exchanging our money with their food. So, it plays a role of medium of exchange in purchasing our food.

On the other hand, unit of account is also a feature of money but it only indicates the price of food at which we are purchasing it. Store of value is used when we store our money as a wealth, then it becomes store of value .

Hence, medium of exchange is the correct answer.

truck y has a greater velocity than truck x.