The consumer's net income is the difference between the price a consumer is willing to pay to obtain a product and the actual price he paid to obtain the product. The consumer's net income measures the additional benefits that the buyer feels he has received. Based on the above definitions, Which of the following options reflect consumer net income:. ['Ms. Li just issued a monthly salary of 4,000 yuan, and plans to use all the money to buy clothes. After shopping in the mall on the weekend, I found that 1,000 yuan was left unfinished.', 'a home buyer pays the monthly mortgage payment with a monthly salary, which is deducted directly from the salary card on a regular basis, leaving 500 yuan a month.', 'Manager Zhang intends to spend 20,000 yuan to buy a watch he likes, but after price negotiation, the final 18,000 yuan was sold, saving 2,000 yuan over the original.', 'Xiao Liu spent 500 yuan to invite a friend to dinner in a hotel. The hotel finally gave him a 100 yuan return coupon, which can be used at the hotel next time.']