Answer:
It is either B or D, and I believe the answer is D.
Explanation:
Deepwater drilling relies on mud being pumped into the drill well for pressure purposes. Without the mud, gas and oil would just rise up uncontrollably because without counteracting the pressure from the sea and the rock, it would be spewing out. The mud helps the drill create the heavy column of downward force needed to maintain control of the output of gas and oil.
The answer choices that would best match the description would be B or D. Since the mud is there for provide pressure and downward force, I would go with choice D as my answer.