When George Everest Took His Gravity Measurements by Dropping a Plumb

When George Everest took his gravity measurements by dropping a plumb line along the flank of a mountain range, he expected the mountain to attract the plumb line from vertical toward the range due to density differences. Instead, calculations later done by John Pratt showed that the plumb line experienced far less attraction toward the mountain than expected. It was concluded that:

A) The mantle rocks below the mountain range were not as dense as expected.
B) Mountain ranges are very large, dense structures.
C) The rocks under the mountain range have far less density beyond its base than its surrounding rocks.
D) He needed to attach a heavier weight onto his plumb line when suspending it next to a mountain range for it to experience greater attraction.