Answer is A
Explanation: Consumer surplus actually happens when a customer is willing and ready to pay for a particular product than its current market price. It is a measure of the additional benefits a consumer gets after paying for a product even though they are willing to pay more.
For example: Let's assume you want to get a IPhone 8 plus and you value it at $800 dollars, which you are ready to pay, but realise it is sold at $700. When you buy it at $700, the customer surplus is $100, that is a difference between how much you were willing to pay and the price you eventually got it.
Consumer Surplus changes as the equilibrium price of a good rises or falls. If the price of a good rises, the consumer surplus decreases but when the price of the good falls, the consumer surplus increases.