I think its A) A antigens
Heterocyst-forming Cyanobacteria differentiate highly specialized cells to provide fixed nitrogen to the vegetative cells in a filament.
<span>the way that Jenner form his hypothesis from this observation is : he asked what would happen if he deliberately inoculated someone with cowpox fluid from another person
based on that observation he crated an experiment which later proof that you can't get another pox if you already experienced it once</span>
A
would be the right answer
not sure but hopefully
