设某企业职工的年薪函数中，年薪Y不仅与工龄X有关，而且与职工的受教育程度有关。如果受教育程度分为大专及其以下、-找考题网

多项选择题Robert Johnson is the best blues guitarist of all time. There is little information available about this legendary blues guitarist, and the information is as much rumor as fact. What is indisputable, however, is Johnson’s tremendous impact on the world of rock and roll. Some consider Johnson the father of modern rock: His influence extends to artists from Muddy Waters to Led Zeppelin, from the Rolling Stones to the Allman Brothers Band. Eric Clapton has called Johnson the most important blues musician who ever lived. Considering his reputation, it is hard to believe that Johnson recorded only 29 songs before his death in 1938, purportedly at the hands of a jealous husband. He was only 27 years old, yet he left an indelible mark on the music world. Again and again, contemporary rock artists return to Johnson, whose songs capture the very essence of the blues, transforming our pain and suffering with the healing magic of his guitar. Rock music wouldn’t be what it is today without Robert Johnson. According to the passage, from what musical tradition did Robert Johnson emerge? Johnson died in Johnson influenced many rock artists, including Led Zeppelin and the Rolling Stones. Contemporary rock artists turn to Robert Johnson for The most appropriate title for this article would be

设某企业职工的年薪函数中，年薪Y不仅与工龄X有关，而且与职工的受教育程度有关。如果受教育程度分为大专及其以下、本科和研究生3个层次，则该年薪函数应引入虚拟变量的个数为( )。 A. 1个 B. 2个 C. 3个 D. 4个