Concept:Bcc is an email header option used to send a copy of a message to a recipient without revealing that recipient's address to others.
Explanation:Bcc stands for "blind carbon copy".
This option hides the email address of the selected recipient from all other recipients in the email thread.
So, when you add someone in the Bcc field, they receive the message, but their address remains invisible to others.
The other choices are incorrect because "backup", "blank", and "bulk" do not describe this hidden-copy feature.
Only "blind" accurately conveys that the recipient's address is concealed from other recipients.
Answer:C. blind carbon copy