A study examined the effect a person's level of education (high school diploma, 2-year college degree, 4-year college degree, and graduate/advanced degree) has on his or her career happiness. The study involved a random selection of airline industry employees, including airline ticket agents, transportation security officers, baggage handlers, and flight crew personnel. A person's career happiness was de- fined as scores on the Career Happiness Scale, which could range from 40 to 200 with higher scores reflecting higher levels of happiness. In this study, "level of edu- cation" is and "career happiness" is

a. a categorical dependent variable; a continuous independent variable

b. a categorical dependent variable; a categorical independent variable

c. a single-factor categorical independent variable with four levels; a continuous dependent variable

d. a four-factor categorical independent variable; a continuous dependent variable