【单选题】

The vegetative forms of most bacteria axe killed by drying in air, although the different species exhibit pronounced differences in their resistance. The tubercle bacillus is one of the more resistant, and vibrio cholcra is one of the more sensitive to drying In general, the encapsulated organisms are more resistant than the non-encapsulated forms. Spores are quite resistant to drying; the spores of the anthrax bacillus, for example, will germinate alter remaining in a dry condition for years or more. The resistance of the pathogenic forms causing disease of the upper respiratory tract is of particular interest in connection with airborne infection, for the length of time that a droplet remains infective is a result, primarily, of the resistance of the particular microorganism to drying.

Tuberculosis is highly infectious because ______.
A、spores are resistant to drying
B、the causative organism is encapsulated
C、droplets of sputum remain infective for a long time due to the resistance of the organisms to drying
D、none of these