Katie, Mike, Sharon, and Bart are each mixing red and yellow paint to make different shades of orange. The graph represents the relationships of the ratios of red to yellow parts in each paint mixture.

Whose color mixture shows a proportional relationship between the number of parts of red paint and the number of parts of yellow paint?

A.

Bart's mixture

B.

Katie's mixture

C.

Sharon's mixture

D.

Mike's mixture