How the human body defends itself after contracting a foodborne illness?

Asquirrel population lives in an area. over many years, a river in that area grows wider and stronger, eventually forming a canyon. the squirrel populations on the two sides of the canyon can no longer mate with each other and ultimately form distinct species. this is an example of

Which of these is not a nucleotide base found in dna?

What is the membrane that sheath of schwann cell containing cytoplasm and nucleus that encloses myelin