The correct answer is A) exhaust to pressures above atmospheric pressure. Most auxiliary turbines do not require an external source of gland sealing steam because they exhaust to pressures above atmospheric pressure. This means the higher internal pressure in the turbine casing helps to keep air from leaking into the system, negating the need for an external gland sealing steam supply. The other options are incorrect because B) operating at relatively low pressures would still require gland sealing, C) a small amount of axial thrust does not eliminate the need for sealing, and D) carbon packing rings are a sealing method, not a reason why external steam is not required.