The cross section below represents large boulders made of granite, gneiss, and quartzite that are found lying on limestone bedrock near Oswego New.

If no overturning of bedrock has occurred, which statement correctly explains the source of the boulders?
A)The limestone was changed by contact metamorphism caused by a lava flow

B)The limestone bedrock formed under conditions of high heat and pressure

C) Older igneous and metamorphic bedrock that once covered the limestone eroded away, forming the boulders

D) The boulders were transported and deposited on the limestone bedrock by a glacier