Which of the following is the BEST example of social engineering?

Which of the following is the BEST example of social engineering?

A.
Posting confidential company information on a public social networking website.

B.
Searching through trash cans and dumpsters to find users’ passwords and confidential information.

C.
Calling random phone numbers and asking customers to purchase a product.

D.
Posing as a member of an IT department and asking a user for their login account information.