London is the most diverse city in the world, with more than 300 languages    16    in the city and  people of 50 nationalities    17    there. What are the causes underlying London’s ethnic diversity? One is that London is a business center so that people all over the world come here to find jobs and    18    money. But the cause that makes people    19    in London is language, because they want their children to build up the    20    in English, which is a great gift and advantage in the global context.    21    cause is surprising. Londoners tend to leave people    22   , and this gives newcomers much space to live their own lives. Finally, food is also an important cause bringing people all over the world to London. Londoner’s    23    for foreign food creates    24    of job for new communities, which invites more foreigners, and at the same time more foreign    25    , into the city.

       While the hat rule certainly feels antiquated, it also begs the question: Why do we do this? After all, there’s nothing about hats that seems inherently offensive. To ensure you’re up to speed on this old etiquette rule, we’ve uncovered the real reason why it’s considered rude to wear a hat indoors.                     According to the etiquette experts over at the Emily Post Institute, the act of removing your hat indoors is a longtime sign of respect. In fact, it probably began with medievalknights. Back in Medieval Europe, any knight who failed to remove his helmet or lift his visor to identify himself could face fatal consequences. Knights also removed their helmets as a sign of vulnerability and trust in churches and in the presence of women and royalty. The rule also has roots in Christianity, as it’s considered customary for men to remove their hats upon entering a church. But perhaps the strictest rules of Western hat etiquette exist in the U.S. Flag Code, which advises men to take off their hats during the national anthem. While the flag code is certainly not a law but an advisory, its inclusion of hat etiquette cements the idea that wearing a hat in the wrong situation is the epitome of rudeness. 　　

       There are a few exceptions to these hat-wearing rules. Men are allowed to keep their hats on at indoor athleticevents, on public transportation, in post offices, airports, hotel or office lobbies, and on elevators. And women are allowed to keep their hats on at all of those places, plus in someone’s home, at luncheons, movies, weddings, garden parties, and even during the national anthem. In addition to removing their hats indoors and during the national anthem, men should also remove their toppers at mealtime and while being introduced to someone new. Nowadays, however, many etiquette experts emphasize the importance of trusting your intuition. If you find yourself in a situation where you aim to show respect to others, then it’s best to avoid coming off as rude and simply remove your hat.