【单选题】

The vegetative forms of most bacteria are 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 cholera 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 after remaining in a dry condition for ten 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.

According to the passage, the risk of infection from airborne microorganisms would likely be greater during a ______.A．heatwave
B．time of high humidity
C．windless period
D．shortage of fuel oil