1) Mountains are formed through various geological processes, including tectonic plate movements, volcanic activity, and erosion.

2) The hamburger, consisting of a ground beef patty served between two buns, is an iconic American food. It has gained global popularity and countless variations, from classic cheeseburgers to gourmet creations with unique toppings and sauces. The invention of the hamburger is often attributed to Louis Lassen, a Danish immigrant in Connecticut, who served the first hamburger in the early 20th century. Today, hamburgers are a staple in fast-food chains, casual diners, and backyard barbecues around the world.

3) The musical "The Phantom of the Opera" has been running in London's West End since 1986, making it the longest-running musical in history.

4) Democracy is a system of government in which power is vested in the people, who exercise it through elected representatives. It allows for political participation, freedom of speech, and protection of individual rights and liberties.