听力原文： How many of you drink cola? Nearly everybody. Do you know that cola started out not as a soft drink but as a cure for headaches back in the late 1800's? John St. Pamberton, a druggist from Atlanta, had experimented for many months trying to find a cure for the common headache. He worked in his backyard, mixing and heating different combinations of oils and flavors until he found one that seemed promising. Pamberton bottled the mixture and began selling it in drugstores as a concentrated syrup that the customer had to mix with water before drinking. Cola's transformation from a medical syrup to a carbonated soft drink came about quite by accident. One day, a customer came into a drugstore complaining of a headache and asked for a bottle of cola syrup. He wanted to take it right away. So he asked the clerk to mix the medicine while he waited. The clerk, instead of walking to the other end of the counter to get plain water, suggested mixing the syrup with soda water. The customer agreed, and after drinking it, remarked how good it tasted. The clerk continued offering the mixture and carbonated cola grew in popularity. Today carbonated colas are sold in most countries around the world. And although they no longer contain the ingredients used to cure headaches, they are still very refreshing. What does the monologue mainly discuss?