Select the correct answer.
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}