Explanation:

- Income: A flow variable. It measures the money received over a period of time, like a monthly salary.

- Wealth: A stock variable. It represents the total value of assets owned at a specific point in time.

- Saving: A flow variable. It refers to the portion of income that is not consumed, saved over a period like a year.

- Investment: A flow variable. It indicates the expenditure on capital goods over a time frame.

Wealth is the correct answer as it is a stock variable and not a flow variable.