In 1775 Jenner began to study the relationship between cowpox (a comparatively harmless disease) and the more dangerous and disfiguring smallpox. ... He hypothesized that exposure to cowpox rendered the body immune from smallpox. After nearly twenty years of experiments, he developed the first vaccine.
6 billion AU is how far the Milky Way is from this galaxy.
A: Scientists have different opinions on its structure.
Explanation:
Hopefully this helps!
I’m pretty sure this is right, good luck