What is the purpose of the & character at the end of a command line?

What is the purpose of the & character at the end of a command line?

A.
It causes standard error to be unbuffered.

B.
It causes the command to be run in the background of the current shell.

C.
It puts the command under the job control facilities of the current shell.

D.
It causes the command to be run as a child of the initial login shell of the user.