(a) Which statement below is an example of an equal-interval variable? A. An equal-interval variable is a numeric variable in which differences between values correspond to differences in the underlying thing being measured. An example of an equal-interval variable is the position finished in a marathon by a runner. B. An equal-interval variable is a numeric variable in which all the variables being measured are equal in value. An example of an equal-interval variable is the age of all 30 year old men in a town. C. An equal-interval variable is a numeric variable in which values correspond to a relative position of things measured. An example of an equal-interval variable is weight. D. An equal-interval variable is a numeric variable in which differences between values correspond to differences in the underlying thing being measured. An example of an equal-interval variable is age