Which of the following are types of social engineering attacks?

An unauthorized person gains entrance to the building where the company's database server resides and accesses the server by pretending to be an employee.

An unauthorized person inserts an intermediary software or program between two communicating hosts to listen to and modify the communication packets passing between the two hosts.

An unauthorized person calls a user and pretends to be a system administrator in order to get the user's password.

An unauthorized person modifies packet headers by using someone else's IP address to hide his identity.