The characteristic unique to the Inca civilization among the options provided is:
B. the practice of sacrificing humans.
While other Mesoamerican civilizations, such as the Aztecs, are well known for human sacrifice, the Inca civilization had a unique and specific way of conducting sacrifices, which included child sacrifice in certain religious rituals.
The other options (A, C, and D) were characteristics shared by various Mesoamerican civilizations, not unique to the Incas.