What is the root of the American jazzA．Songs sung

单项选择题

American Jazz
Jazz is a gift to the world from the American blacks. It is rooted in the music that the black slaves sang as they picked cotton in Alabama, or heaped up the earth on the levees along the Mississippi River. This strange rhythmic chanting, with its African harmonies, was encouraged by the white masters, who knew that it helped to get the work done.
In the 1790s the Methodists, a Protestant sect, began to convert the slaves to Christianity, so that during the 19th century most of the blacks became Protestants of one denomination or another. Led by their own black ministers, they worshipped in their own black churches—or out in the open air. Music played an essential part in the service. Before long they had Africanized the music of the Christian hymnbooks.
It was the feelings of the slaves in 1865 which finally brought black musicians into the world of entertainment, making music a way of earning a living. In the great port of New Orleans, bands of self-taught black trumpeters, clarinetists, drummers, pianists, found work of another kind. New Orleans was a colorful, pleasure-loving, cosmopolitan city, and a flourishing "red light" district had grown up there. This improvised music, with its exciting syncopated rhythms, its "African" harmonies, its expression of emotion and mood, became known as jazz.
In 1917 the "red light" district of New Orleans was shut down. The USA had entered World War Ⅰ and the US Navy was afraid of the effect of the "houses" might have on its sailors. Black musicians lost their jobs. But not for long! Many of them left New Orleans—and jazz exploded into the world outside.
Many went north up the Mississippi to Chicago, where a large black population was already living on the South side. Jazz musicians thrived in the "speakeasies". Some of the most famous jazz players began their careers in Chicago. The trumpeters, Joe "King" Oliver and Louis Armstrong, both came from New Orleans and matured in Chicago. Louis Armstrong did more to promote jazz than any other single musician. Jazz later reached Broadway, where it became big business. In the 1920s jazz became a craze. After the honors and tensions of World War Ⅰ, people wanted to have fun. The strong, exciting rhythms of jazz set everyone dancing. White dance bands played loud and feverish music in the dance halls and fashionable restaurants. But soon this ceased to be true jazz; it was jazz adapted to suit the needs of the dances. But the original jazz has never died, and there is a great interest in it today. There are jazz concerts and jazz festivals all over the world.
In New Orleans, black bands, white bands and mixed bands still play in the jazz halls of the old quarter. New Orleans is devoted to the preservation of jazz. One of the favorite haunts of jazz lovers in New Orleans is called Preservation Hall, a scruffy little room whose walls are decorated with faded prints and photos of the great players of the past.

What is the root of the American jazz

A．Songs sung by the American black slaves.
B．Songs sung by the white masters.
C．Songs sung by the African black people.
D．Songs sung by the African black slaves.