Commodity difference: The price difference of the same product due to different circulation links, purchasing and selling regions, purchasing and selling seasons, and different quality. Which of the following is not a commodity spread? ['The same book has a different price when it is first published than two years later.', 'One pound of radish in the morning market, and fifty cents in the afternoon.', 'Fukang sedan differs in price from Volkswagen.', 'Salt inland A is cheaper than salt inland B because.']