Which of the following is placed in an application by programmers either knowingly or inadvertently to bypass normal authentication?

A. Input validation
B. Sandbox
C. Back door
D. Virus

C. A backdoor is placed within applications, operating systems, and network devices to bypass normal authentication. Input validation is a process that ensures the correct usage of data and is commonly used by programmers and developers. A sandbox is when a web script runs in its own environment. A virus is a malicious piece of code that can cause damage to a computer if it is opened and executed by a user.