Which of the following is the most important element of Koch’s germ theory of disease? The animal shows disease symptoms when ( )
选项:
A: the animal has been in contact with a sick animal.
B: the animal has a lowered resistance.
C: a microorganism is observed in the animal.
D: a microorganism is inoculated into the animal.
发布时间:2024-05-18 21:01:06