Which of these best describes what a pie chart shows?
a. how two quantities compare to each other
b. the influence of one variable on another
c. the way that a single variable grows over time
d. a pie chart is a circle and shows parts of a whole

D, because a pie chart show the subsets of a whole unit.
It is not a because that would be a Venn diagram.
It is not b because a pie chart does not include how a variable affects another variable.
And it is not c because it does not show how a variable change but it shows how much of a variable there is. 

It is the poet alfred, lord tennyson himself