To prove her claim that the number of pages she has read (y) is proportional to the number of minutes she has spent reading (x), Sara would need to demonstrate that there is a consistent ratio between y and x, indicating that they are indeed proportional.
The best action she could take from the given options would be:
D. Plot the coordinate pairs on a graph and show that the points make a straight line through the origin.
This action would visually demonstrate that the relationship between the pages read and the minutes spent reading is indeed proportional since a line through the origin indicates a constant ratio (a direct variation) between the two variables.
Other options, such as A and B, do not support the claim of proportionality effectively, and option C would not conclusively demonstrate a consistent proportional relationship without further verification. Therefore, option D is the most effective choice for proving the claim.