The Clue Mouth-to-mouth is part of it: Abbr.
The Answer CPR
The clue "Mouth-to-mouth is part of it: Abbr." refers to CPR, which stands for cardiopulmonary resuscitation. CPR is a lifesaving technique that includes mouth-to-mouth breathing as one of its steps. This method helps provide oxygen to someone who has stopped breathing. Therefore, "CPR" is the correct abbreviation that fits the clue.