单项选择题

C

If an American is satisfied with you, he will put his thumb and forefinger into a circle. That means OK. But in Brazil, the very sign is considered to be rude. In Poland, a guest usually presents flowers to his hostess. The number must be an odd (奇数) one. Besides, the hostess isn’t expected to remove the cover of the bunch of flowers. And usually, red rose is a sign of love. Usually we nod to express our agreement and shake our heads to show disapproval. To our surprise these body movements mean the opposite in Bulgaria (保加利亚). The differences in customs and cultures in the world are really noticeable. We should learn more about them to avoid embarrassment (窘迫). Then, would you please remember: When in Rome, do as the Romans do.

The sentence "When in Rome, do as the Romans do" means that ______.