Which statements are true?

choose exactly two answers that are correct.

dentist mean patient age mad
appiah 43 9.7
cantwell 29 13.9
singh 41 14.1

a.
dr. appiah’s patients’ ages vary more than do dr. cantwell’s patients’ ages.

b.
dr. appiah’s patients’ ages vary less than do dr. singh’s patients’ ages.

c.
dr. cantwell’s patients’ ages and dr. singh’s patients’ ages vary about the same amount.

d.
dr. singh’s patients’ ages and dr. appiah’s patients’ ages vary about the same amount.