What Is the Primary Difference Between a Worm and a Virus

What is the primary difference between a worm and a virus?

A) A worm must attach to something to spread, where a virus does not need to attach to anything to spread and can tunnel itself into the computer
B) A virus is copied and spread by a person, where a worm takes a string of tag words and deletes websites
C) A virus must attach to something to spread, where a worm does not need to attach to anything to spread and can tunnel itself into the computer
D) All of the above