John and Linda Are Arguing About the Definition of Density

John and Linda are arguing about the definition of density. John says the density of an object is proportional to its mass. Linda says the object's mass is proportional to its density and to its volume. Which one, if either, is correct?

A) They are both wrong.
B) John is correct, but Linda is wrong.
C) John is wrong, but Linda is correct.
D) They are both correct.
E) They are free to redefine density as they wish.