What is steganography and in what file types is it commonly used?

Group of answer choices

It$$s a method of encrypting text and is used mainly in $.$txt files.

It$$s the practice of secure key exchange typically used in $.$key files.

It$$s the process of concealing messages within digital files, commonly used in formats like $.$bmp$,.$wav, $.$mp$3,$ and $.$au$.$

It$$s a network protocol used for secure data transfer in $.$ftp files.