Tea is made from the leaves of a plant that grows well in warm, wet places. Legend says that it was first discovered in China, and people there have drunk it for a very long time. Black tea and green tea come from the same plant; the difference is in how the leaves are treated after picking. For black tea, the leaves are left to darken in the air, while for green tea they are heated quickly to keep their color. In many Arab countries, tea is served strong and sweet, often with mint, as a sign of welcome, and offering it to a guest is an important custom. In Britain, people often add milk. Tea contains caffeine, but usually less than coffee, so many people find it a gentler drink.

Question: Why is tea offered to a guest in many Arab countries?