To assess lung sounds.

Choice A rationale:

Sterile suctioning is not performed to administer medications. Its primary purpose is to remove secretions and maintain a patent airway.

Choice B rationale:

Sterile suctioning is not done solely for promoting comfort. Its main goal is to clear the airway and prevent respiratory complications.

Choice C rationale:

The purpose of sterile suctioning is to assess lung sounds by removing excess secretions and mucus that may obstruct the airway. This helps in evaluating the patient's respiratory status and identifying any abnormal lung sounds.

Choice D rationale:

Sterile suctioning is not performed to monitor vital signs. Although vital signs may be monitored during the procedure, it is not the primary purpose of suctioning.