Men could directly turn back to Greece and Rome for instruction, for correction, and for inspiration in the following riel& of their work except

A．Plants that infest human habitations
B．the fact that bacteria are really vegetables
C．the growing stage of the bacteria as opposed to the dormant stage
D．the difficulty in classifying the types of bacteria

A．heat wave
B．time of high humidity
C．windless period
D．shortage of fuel oil