What about Nga's second receipt?

Nga's second-order welfare is too hot. The second order is to sell a product for free or at an ultra-low price at a certain point in time, but the time is very short, and the things sold are limited, and you can't grab it quickly or slowly. The price of the goods sold at this time is the spike price. Spike price first appeared in China, which refers to snapping up certain limited discount goods in a limited time.