The term tile (called azulejo) comes from the Arabic word az-zulayj, meaning“polished stone.” The Moors, a member of the Muslim population, first brought thisterm to Portugal during their occupation. Although tiles are not a Portuguese invention,they have been used more imaginatively and consistently in Portugal than in any othernation. By the 18th century, Portugal produced tiles for a variety of purposes and inmany different designs. Today, they still remain a very important part of the country’sarchitecture. Tiles often portray scenes from the history of this Western Europeancountry, show its most stunning sights, or simply serve as street signs, nameplates, orhouse numbers.    In the 15th century, Spain had a great influence on Portuguese azulejos when KingManuel I decorated his palace with the same rich ceramic tiles as the ones he saw inthe Alhambra palace of southern Spain. The first tiles were imported to Portugal, andthey portrayed no human figures, only geometric patterns.    In the 16th century, Portuguese artists began to produce tiles in their own country.Blue and yellow were the favorite color combination and tiles depicted mostly floralpatterns or religious scenes. As the Portuguese empire expanded, more exotic themesand colors were adopted to make tiles. Towards the end of the 17th century blue tilesbecame popular. This was probably due to the craze for blue and white porcelain fromChina, which was being imported into Europe at this time.    After the earthquake of 1755, there was a return to multi-colored tiles. It was aboutthis time too that tiles were found to be an ideal construction material because theyhelp to keep the damp out of buildings. In Lisbon, the rebuilt houses were covered intiles, and this tradition continues today.    In the early 20th century, azulejo art had fallen out of favor. The cultural elitedespised it and thought it was for poor people. But an azulejo revival started in the1950s, when Lisbon’s first metro station designers wanted a low-maintenance, easyway to have the underground spaces feel less separate from the outside world. Sincethen, tile art has been installed in numerous other metro stations.
21. What is the main idea of the first paragraph?
(A) Tiles function to advertise famous tourist attractions in Portugal.
(B) Tiles are used commonly to decorate public buildings in Portugal.
(C) Tiles depict important historical events that happened in Portugal.
(D) Tiles serve various purposes and come in different designs in Portugal.