Write an Introduction about explaining the Coronavirus to someone from the past?

We have had a lot of troubles in the past. World Wars, Flu epidemics. Countries have changed. Countries allied each other to defeat others. But the only time when all the countries come together to defeat the same enemy -- Corona virus.

answer: hmm i’ve done that before.. i’ll answer back when i move got it. i know i have the answer.. it’s on the tip of my tongue! don’t worry.. i’ll try to answer asap!

explanation:

- "the basic difference between keywords and subjects is that subjects (or "subject headings") have been predetermined, while keywords have not. a keyword is an easy place to start because you can use any word that seems to fit your search; this is called "natural language" searching."