The element that supports the weight of the drill stem, allows the drill stem to rotate, and provides a pressure-tight seal and passageway for the drilling mud to be pumped down the inside of the drill stem is called the __________.

Correct Answer: Option D — swivel

The swivel is a critical component in the rotary drilling string. It provides a mechanical suspension point for the drill stem, allows for continuous rotation during drilling operations, and features a high-pressure packing assembly that facilitates the circulation of drilling mud from the standpipe into the rotating drill string.