The correct answer is: A. Stock concept.
A stock is a quantity of something that is available at a particular time. In economics, a stock is a measure of the amount of a good or service that is available at a given time. The supply of a commodity is the total amount of that commodity that is available for purchase at a given price.
A flow is a measure of the rate at which something changes over time. In economics, a flow is a measure of the amount of a good or service that is produced or consumed over a period of time. The supply of a commodity is not a flow because it does not measure the rate at which the commodity is produced or consumed. It measures the total amount of the commodity that is available for purchase at a given time.
The other options are incorrect because they do not accurately describe the supply of a commodity. Option B, “Flow concept,” is incorrect because the supply of a commodity is not a flow. Option C, “Both stock and flow concept,” is incorrect because the supply of a commodity is not both a stock and a flow. Option D, “None of the above,” is incorrect because the supply of a commodity is a stock concept.