下列有关磨制石器的叙述，正确的是    （    ）    

人体体液中存在着许多酸碱缓冲对（如H₂CO₂与HCO₃^-、 HPO₄^2-与H₂PO₄^-等），它们既能与酸性物质发生反应，又能与碱性物质发生反应，这说明无机盐

    Mike is a football fan. There is a football match between Chinese team and American team. He wants to watch it. He comes to the box office and gives the clerk 10 yuan. The clerk says, “Please give me another 10 yuan. The price of a ticket is 20 yuan.”

    “Why?” says Mike, “I just watch Chinese team. I don't want to watch the other team at all. Do you want me to buy a ticket for it?No, no, no...”