It’s the 3rd one! The O + O!!
I do believe that it is both naturally occurring and caused by human activity. Although science has proven that it is something that naturally progresses with time, humans have sped up the process. Hope this helps:)
Explanation: some cells are specialized to do certain stuff. Like the breaking down of glucose wouldn't happen in the cells found in your leg.
<span>Herpesviridae is a large family of DNA viruses that cause diseases in animals, including humans.
When a person infected once, his immune system develops antidot against the virus, so he becomes immune for that virus for rest of his life. In other words, he can't be affected from that virus again
Hope this helps!</span>
