The flag, the most common symbol of a nation in the modern world, is also one of the most ancient. With a clear symbolic meaning, the flag in the traditional form is still used today to mark buildings, ships and other vehicles related to a country. The national flag as we know it today is in no way a primitive artifact. It is, rather, the product of thousands of years' development. Historians believe that it had two major ancestors, of which the earlier served to show wind direction. Early human beings used very fragile houses and boats. Often strong winds would tear roofs from houses or cause high waves that endangered travelers. People's food supplies were similarly _ . Even after they had learned how to plant grains, they still needed help from nature to ensure good harvests. Therefore they feared and depended on the power of the wind, which could bring warmth from one direction and cold from another. Using a simple piece of cloth tied to the top of a post to tell the direction of the wind was more dependable than earlier methods, such as watching the rising of smoke from a fire. The connection of the flag with heavenly power was therefore reasonable. Early human societies began to fix long pieces of cloth to the tops of totems   before carrying them into battle. They believed that the power of the wind would be added to the good wishes of the gods and ancestors represented by the totems themselves. These flags developed very slowly into modern flags. The first known flag of a nation or a ruler was unmarked. The king of China around 1000 B.C. was known to have a white flag carried ahead of him. This practice might have been learned from Egyptians even further in the past, but it was from China that it spread over trade routes through India, then across Arab lands, and finally to Europe, where it met up with the other ancestor of the national flag. The earliest flags were connected with heavenly power because   _  .
they could tell direction they could bring good luck to ancient fighters they were handed down by the ancestors they were believed to stand for natural forces