An example of the use of acid-fast staining is the staining of bacteria that have mycolic acids in their membrane, also called acid-fast bacteria because they resist unstaining with this acid-alcohol mixture. Because of this characteristic, such bacteria are not gram-stained. Therefore, B is not the answer.
To perform this staining you must first make a smear of the bacteria and fix it on the slide and then stain it. The immersion in acid alcohol is done during the staining process and the observation under the immersion lens at the end of the staining. Therefore, the answer is C
