Answer:
Spread
Explanation:
People use envelopes very often. The germs people carry are put into the envelope and then it's sent out to many others.
Viruses need to be inside a living thing (of course the living thing has to have the right temperature which most living things do) . When they're inside a living thing they start injecting the host's cells with its DNA in order to make more copies of itself which allows the virus to spread. So basically viruses need to be inside something living.
