Silicates is the answer to this.
O2 or Oxygen gas is released into the environment as a result of photosynthesis.
B) Peyer’s patches. Located in the mucosa and extend to the submucosa of the small intestine
I think the reservoir ( a human,animal or non living such as soil where the infectious agent normally lives)
secondly the mode of transmission,there are some modes of transmission that allow the pathogen to enter quickly and some that make the process slow.
and also crowding and the presence of co-infections.
i hope this helps