The most accurate statement is:
"Money does not provide a standard unit of measurement."
However, upon reviewing the other options, none of them accurately describe the nature of money. Money can fluctuate in value over time due to inflation and other economic factors, which means it does not retain its purchasing power permanently or maintain a constant value.
If you are looking for the true statement based on general understanding, it could be phrased that "money can fluctuate in value and does not retain purchasing power over time."