Roundworms have taken this last body plan and adapted to thousands of environments with it. From microscopic to maybe a meter long, roundworms are just what they sound like-round worms. At one end, they have a mouth, at the other, an anus, with a tube digestive system in between.
Availability of two-factor authentication for Apple ID Two-factor authentication is an extra layer of security for your Apple ID designed to ensure that you're the only person who can access your account, even if someone knows your password.
Four-factor authentication is a newer security paradigm than two-factor or three-factor authentication. Four factor systems are sometimes used in businesses and government agencies that require extremely high security. Knowledge factors include all things a user must know in order to log in, such as a user name and password or personal identification number (PIN). 2  Possession factors include anything a user must have in their possession to log in, such as a one-time password token (OTP token) or a smartphone with an OTP app.