The Demand for Oil Rig Workers Off the Coast of Louisiana

The demand for oil rig workers off the coast of Louisiana is the same as the demand for oil pipeline workers in North Dakota. The annual earnings of Louisiana oil rig workers is 22% higher than the earnings of North Dakota oil pipeline workers. A possible explanation for this is

A) Louisiana oil rig workers can work only part of the year, but North Dakota oil pipeline workers can work year round.
B) the amount of human capital needed to be a pipeline worker must be greater than the amount of human capital necessary to be an oil rig worker.
C) Louisiana oil rig workers must face discrimination that is not encountered by North Dakota oil pipeline workers.
D) being an oil rig worker in Louisiana must be more dangerous than being a pipeline worker in North Dakota.