PIN Stands for Personal Identification Number, as the name states it is a combination of numbers. The following answers are incorrect:
User ID This is incorrect because a Userid is not required to be a number and a Userid is only used to establish identity not verify it. Password. This is incorrect because a password is not required to be a number, it could be any combination of characters. Challenge. This is incorrect because a challenge is not defined as a number, it could be anything.