Which data set has the greatest spread? set a – {84, 91, 87, 77, 94, 89, 74} set b – {89, 73, 84, 91, 87, 77, 94} set c – {73, 84, 89, 88, 77, 91, 87, 90} set d – {84, 89, 88, 82, 91, 87, 99} a. set a b. set b c. set c d. set d