read the text change the words on the right to complete it (4упражнение)

Sometimes jazz concerts are broadcast on the radio and on television. We(1) are sure that you (2) 've heard about this type of music. It (3) appeared in the United States when the (4) first Africans (5) were brought to North America. In those years many native songs (6) were sung by (7) them and the music of (8) their homeland (9) was played on the new continent. Modern (10) scientists write that jazz (11) is made up of the music of West Africa.