C. Room attendant.
An introvert is typically someone who is not very comfortable interacting with people, at least not for extended periods of time. Therefore, a good job position for an introvert would involve working alone.
Room attendant is the only job in the list in which one would not be in contact with colleagues or customers most of the time. A room attendant's main responsibilities would be to clean hotel rooms and public areas, and to keep them ready for customers according to the lodging establishment's standards.
The position can be obtained with a high school diploma, as many hotels provide initial training upon recruitment.