Which of the following combines something you know, such as a password, with something you are (a biometric device such as a fingerprint or a retina scan) or something you possess (a smart card or a USB stick)?.a. Confidentiality b. Authentication c. Two-factor authentication
d. Third-party certificate system

c. Two-factor authentication

Explanation:

Two-factor authentication is also known as 2FA. It is an extra form of security put in place aside the use of username and password to ensure the authenticity of someone trying to access an online platform with a registered account.

First the user enters his or her username and password, then they will also have to provide some extra information before finally gaining access. Such information could be ones place of birth, name of pet, something one has or know, etc.

2FA helps to still keep an account safe even if a device or password is been stolen. Two-factor authentication could be SMSbased, hardware token, software token, etc.

i believe the two important functions that skype uses are nat traversal and user location.good luck        

explanation:

what class is it and how much will you pay?