Oil Shale Contains Kerogen Rather Than Oil Because

Oil shale contains kerogen rather than oil because:

A) it was never buried deeply enough to raise its temperature to that required to produce oil.
B) shale is not permeable enough to allow the kerogen to move freely through the rock.
C) there has not been sufficient time for further breakdown of the large kerogen molecules.
D) the organisms required to produce oil were never deposited within the shale.