Answer:
Checking the price of a camera at several stores before buying it. Option C is correct.
Step-by-step explanation:
The other options do not necessarily involve using the money as a unit of account. Opening a savings account at a bank consists in using money as a store of value; lending a friend $25 is termed as a medium of exchange of money, and purchasing a toy also falls in the same category as option A. Option C is correct because a person is comparing the price of the camera at several stores and using money as a way to measure and compare the values of the camera.