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.

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Answer: B