Which of the following did Mary buy for her grandparents this year?

　　定位到文中第四段的第三句，“The white ones were sour. The star grapefruit were interesting, but the dark red grapefruit were great. So she got a kilogram.” 白色的是酸的。葡萄柚也很不错，但是深红色的葡萄柚很棒。所以她买了一公斤。故选B。