Using the Rule of Thumb for Elevations and the Information

Multiple Choice

Using the rule of thumb for elevations and the information provided by the image, what may be said of the actual differences in elevation and crust thickness between Phoenix and Flagstaff Elevation Phoenix: 300 m, Flagstaff: 2100 m) ?

A) The differences are what we would predict. Rule of thumb: increase of 6 km crust thickness = increase in 1 km elevation.
B) The differences are what we would predict. Rule of thumb: increase of 1 km crust thickness = increase in 6 km elevation.
C) The differences are not what we would predict. Rule of thumb: increase of 1 km crust thickness = increase in 1 km elevation.
D) The differences are not what we would predict. Rule of thumb: increase of 6 km crust thickness = increase in 6 km elevation.