a) Pneumonia, diphtheria, chicken pox, cholera.
Odd word: Chicken pox
Because chicken pox is a viral disease while all the other are bacterial disease.
b) Lactobacilli, rhizobia, yeast, clostridia
Odd word: rhizobia
Because rhizobia is the bacteria found in plants while all the other are the bacteria related to human food products.
c) Root rot, rust, rubella, mozaic
Odd word: rubella
Because rubella is the human disease while all the other are the diseases found in plants.