The answer is B. Mainstream smoke.
Reasoning: it's putting your lips up to the butt of the cigarette and inhaling straight from the MAIN source of the nicotine and tobacco. So, it is mainstream smoking.
Secondhand smoking is breathing in the smoke that comes from the mainstream smoker, sidestream smoking is breathing in the smoke that comes from the burning cigarette, and passive smoking is breathing in the smoke from the mainstream smoker involuntarily, such as walking into a room and having smoke blown in your face.