Concept:Supply measures the quantity of a good that sellers can offer over a specific period of time.
This makes supply a flow variable, not a stock variable.
Explanation:In economics, a flow is measured per unit of time, for example output per month or per year.
A stock is measured at a particular point in time, such as the quantity of goods in a warehouse today.
Because supply is always expressed with reference to a time dimension, it can change continuously within that time period.
Therefore, supply has the same nature as income or production, which are flows.
This is why supply is described as a flow rather than a stock, constant, or a mere table.
Answer:B. A flow