10. A study examined the effect level of education (high school diploma, 2-year college degree, 4-year college degree, and graduate/advanced degree) has on career hap- piness. The study involved a random selection of people working in the aviation in- dustry, including airline ticket agents, security officers, baggage handlers, and pilots. A person's career happiness was defined as scores on the Career Happiness Rating Scale and could range from 40 to 200; the higher the score, the happier the individual. In this study, "level of education" is considered and "career happiness" is considered

a. the dependent variable, the independent variable

b. the dependent variable, a nominal variable

c. the independent variable, a continuous variable

d. a discrete variable, a Likert variable