There's a whole lot of things that people fill their stomachs with. Some of them keep people alive. Some of them taste good to people. Some of them help people win pie-eating contests. Alcohol does none of these things. Why do people keep drinking it? And what does it do once it gets to their stomachs? There are all kinds of alcohol molecules  , but the one that people most often pour down their throat is ethanol  . Ethanol is very tiny and it dissolves in water, so it gets into all sorts of places that it's not supposed to. Alcohol heads for the digestive system. Because it dissolves in water, it can get into the water in the bloodstream. Because ethanol, to a certain extent, can pass through cell membranes . It can go almost anywhere. It spreads through the muscles, and is sweated -- unmetabolized  and whole -- through the skin. It gets into the heart. It even takes a walk through the brain, and this is the secret of its powers. Alcohol depresses the nerves, and the nerves affect almost every area of the body. Enough alcohol makes people sleep, so people who become unconscious choke on their own vomit  . Most worryingly, enough alcohol can shut down those parts of the brain just like any other parts. People become unconscious and their brains simply forget to breathe. Alcohol is broken down in the liver. Alcohol doesn't destroy the liver, but products that the liver breaks the alcohol into do cause damage. A glass of wine per day can not do any harm. Instead, it can prevent heart attacks or can make someone functionally young. And it is kind of nice to know that sometimes, relaxation and cheer can be bottled. All that's needed is to take care how much alcohol is let into a person's brain. How does the author introduce the topic of the text?
By statement. By question. By arguing. By explaining.