Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions that follow

Line (5)           (10)	Jazz has been called “the art of expression set to music”, and “America’s great contribution to music”. It has functioned as popular art and enjoyed periods of fairly widespread public response, in the “jazz age” of the Line 1920s, in the “swing era” of the late 1930s and in the peak popularity of modern jazz in the late 1950s. The standard legend about Jazz is that it originated around the end of the 19th century in New Orleans and moved up the Mississippi River to Memphis, St. Louis, and finally to Chicago. It welded together the elements of Ragtime, marching band music, and the Blues. However, the influences of what led to those early sounds goes back (10)________to tribal African drum beats and European musical structures. Buddy Bolden, a New Orleans barber and cornet player, is generally considered to have been the first real Jazz musician, around 1891.
(15)           (20)	What made Jazz significantly different from the other earlier forms of music was the use of improvisation. Jazz displayed a break from traditional (15)________music where composers wrote an entire piece of music on paper, leaving the musicians to break their backs playing exactly what was written on the score. In a Jazz piece, however, the song is simply a starting point, or sort of skeletal guide for the Jazz musicians to improvise around. Actually, many of the early Jazz musicians were bad sight readers and some couldn’t even read (20)________music at all. Generally speaking, these early musicians couldn’t make very much money and were stuck working menial jobs to make a living. The second wave of New Orleans Jazz musicians included such memorable players as Joe Oliver, Kid Ory, and Jelly Roll Morton. These men formed small bands and took the music of earlier musicians, improved its complexity, and gained greater success. This music is known as “hot Jazz” (25)________due to the enormously fast speeds and rhythmic drive.
(25)	A young cornet player by the name of Louis Armstrong was discovered by Joe Oliver in New Orleans. He soon grew up to become one of the greatest and most successful musicians of all time, and later one of the biggest stars in the world. The impact of Armstrong and other talented early Jazz musicians changed the way we look at music.

The word “their” in line 15 refers to which of the following?