Why Is It Important to Use the Huff's Gravity Model

Why is it important to use the Huff's Gravity Model in conjunction with the analog and regression methods?

A) The Huff's model does not utilize demographic variables.
B) The analog and regression methods consider too many variables other than demographic.
C) There has been additional supportive research since the Huff's model that can supplement the findings of the Huff's model.
D) The Huff's model only offers comparative data and is unable to assist in choosing specific sites.
E) The Huff's model only offers information about income levels in comparison to the size of the shopping area.