题目

Peter loved to shop used articles. Almost a month ago, he bought popular word game that used little pieces of wood with different letters on them. As he was purchasing it, the salesgirl said, “Uh, look, the game box haven’t even been opened yet. That might be worth some money. ” Peter examined the box, and, sure enough, it was completely covered in factory-sealed plastic. And he saw a date of 1973 on the back of the box. “You should put that up for auction (拍卖) on the Internet, and see what happens.”the salesgirl said. “Yes, you’re right. People like something rare. 碘131是碘元素的一种放射性核素。下列关于I的说法正确的是     A．质量数为131         B．质子数为78           C．核外电子数为78    D．中子数为53