The most specific feature of death due to hanging is-
Dribbling of saliva is specific for antemortem hanging.
Tardieu spots are less common in hanging and they are not specific for hanging. They are more common in strangulation.
Fracture of thyroid cartilage is more common in strangulation.
Option b requires specific mention here. Diagnosis of hanging can also be made by ligature mark. But then the option should be 'features of ligature mark', not simply ligature mark, because the ligature mark is seen both in hanging and strangulation. It is the features of ligature mark which differentiates between two.
Tardieu spots
Ligature mark
Fracture of thyroid cartilage
Dribbling of saliva