Other sections of society included the nobility, clergy, and townsmen. Nobles, both the titled nobility and simple knights, exploited the manors and the peasants, although they did not own lands outright but were granted rights to the income from a manor or other lands by an overlord through the system of feudalism. During the 11th and 12th centuries, these lands, or fiefs, came to be considered hereditary, and in most areas they were no longer divisible between all the heirs as had been the case in the early medieval period. Instead, most fiefs and lands went to the eldest son.[R] The dominance of the nobility was built upon its control of the land, its military service as heavy cavalry, control of castles, and various immunities from taxes or other impositions.[S] Castles, initially in wood but later in stone, began to be constructed in the 9th and 10th centuries in response to the disorder of the time, and provided protection from invaders as well as allowing lords defence from rivals. Control of castles allowed the nobles to defy kings or other overlords. Nobles were stratified; kings and the highest-ranking nobility controlled large numbers of commoners and large tracts of land, as well as other nobles. Beneath them, lesser nobles had authority over smaller areas of land and fewer people. Knights were the lowest level of nobility; they controlled but did not own land, and had to serve other nobles.[T]
In what century were castles first built?
9th

Nearly two billion people in the developing world are deficient in zinc. In children it causes an increase in infection and diarrhea, contributing to the death of about 800,000 children worldwide per year. The World Health Organization advocates zinc supplementation for severe malnutrition and diarrhea. Zinc supplements help prevent disease and reduce mortality, especially among children with low birth weight or stunted growth. However, zinc supplements should not be administered alone, because many in the developing world have several deficiencies, and zinc interacts with other micronutrients.
800,000 children worldwide die each year due to what?
deficient in zinc

At the age of 21 he settled in Paris. Thereafter, during the last 18 years of his life, he gave only some 30 public performances, preferring the more intimate atmosphere of the salon. He supported himself by selling his compositions and teaching piano, for which he was in high demand. Chopin formed a friendship with Franz Liszt and was admired by many of his musical contemporaries, including Robert Schumann. In 1835 he obtained French citizenship. After a failed engagement to Maria Wodzińska, from 1837 to 1847 he maintained an often troubled relationship with the French writer George Sand. A brief and unhappy visit to Majorca with Sand in 1838–39 was one of his most productive periods of composition. In his last years, he was financially supported by his admirer Jane Stirling, who also arranged for him to visit Scotland in 1848. Through most of his life, Chopin suffered from poor health. He died in Paris in 1849, probably of tuberculosis.
Where did he end up living when he was 21?
Paris