Ok, so you know that pH is like the alkilinity of something, or how acidic something is. 7 is neutral, and the lower the number, the more acidic. So, if you already know that you put the fruits in order to the proportion of their size, answer D is already wrong, saying that grapefruits are smaller then oranges. Answer B is also wrong, because you also know that the pH will be lower then oranges, not higher. So it will either be A or C. Which one do you think it is?