The correct option is A buy
Demand is the quantity of a commodity that the consumer is able or willing to buy. When we pay the price to buy goods and services, we become the buyer and create a demand.
For example, you buy 5 chocolates for the price of ₹1 per chocolate. So the demand is ₹5. If the price of one chocolate increases to ₹2 rupees, you might buy only 3 chocolates. Then the demand would be 3.