Which of the following is the most commonly used check on something you know?

Which of the following is the most commonly used check on something you know?

A.
One time password

B.
Login phrase

C.
Retinal

D.
Password

Explanation:
Passwords even though they are always mentioned as being unsecured, necessary evils,
that put your infrastructure at risk, are still commonly used and will probably be used

for quite a few years. Good passwords can provide you with a good first line of
defense. Passwords are based on something the user knows. They are used to authenticate
users before they can access specific resources.