You know, I was going to give you props on what a nice thing to say with your beginning statement.....then I read on and realized you are just looking down your nose, like maybe I'm one of your students. Thankfully not, and all I can say if that's the best explanation you can give on a fill in the blank question to your middle school age science class....maybe you need to find another line of work. Because the subject was masks, and another time they were used in mass to try and mitigate was in 1916-1918 with this thing called the Spanish Flu. Have them look up the numbers on that. Not on the internet. In these things called books. Then go back and try to use that same canned explanation of yours with those middle school kids. Because there is no "science" backing masks up now.........just like there wasn't back then.