When the command echo $$ outputs 12942, what is the meaning of 12942?

When the command echo $$ outputs 12942, what is the meaning of 12942?
A . It is the process ID of the echo command.
B . It is the process ID of the current shell.
C . It is the process ID of the last command executed.
D . It is the process ID of the last command which has been placed in the background.

Answer: B