Namazume sake is characterized by which of the following?

Namazume sake is indeed characterized by being bottled as unpasteurized sake that undergoes a single pasteurization process after bottling. This method allows the sake to retain more of its fresh flavors, aromas, and some of the lively characteristics associated with unpasteurized sake, while still ensuring that it is stable and free from undesirable microorganisms.

This process stands in contrast to completely unpasteurized sake, which can be referred to as namazake and tends to have a shorter shelf life due to its raw nature. Similarly, the pasteurization practice noted in the other choices—such as undergoing multiple pasteurizations—would not be true for namazume sake, as that would significantly alter its flavor profile, making it more stable but less fresh.

Additionally, while storing with lees can enhance the complexity of flavors in some types of sake, this is not a defining attribute of namazume. Thus, the unique single pasteurization process employed for namazume sake is what distinctly sets it apart and aligns with the characteristics mentioned in the correct answer.