The correct option is C Pythium
Pseudomonas and Xanthomonas are bacteria. Bacterial cell walls are made of peptidoglycan.
Saccharomyces cerevisiae is a fungus Fungal cell walls are mainly made of chitin.
Based on elimination, and since it is unlikely to know what kind of organism Pythium is, you can conclude that Pythium is the right answer.
In reality, Pythium is kind of fungus that does not have Chitin, but cellulose as a major cell wall component.