Answer:
Speakers.
Explanation: Cause they only output sound, and are devices, further more they are not used to output images, like how could speakers output images using sound? They can't.
The subject is generally covered inside the body of text, so that one's out.
The footer is a completely separate part of the document, specifically the bottom-most portion of the page, but let's look at the others.
The salutation is placed at the beginning of the body of text.
And your closing note is placed at the end of the body of text.
So, the best answer would be b. footer.
The answer in the space provided is the Diffie-Hellman Key
Exchange. This is entitled to be the first published key algorithm in which has
a limit in which the exchange occurs in secret values and that its purpose was
to enable two users to have an exchange of key in a secure manner in means of
using it for a subsequent symmetric encryption in terms of messages.
To make sure you studied everything you need to know.