Which variable can a mean and standard deviation be calculated?

A. Level of education (12th Grade or less; Associate's Degree; College Degree; Graduate school)

B. Age reported in years

C. Income (< $40,000; $40,000-$60,000; $60,000-$80,000; > 80,000)

D. Family race/ethnicity (White; Hispanic; Black; Asian/Pacific Islander)