Mode is best$-$suited as a measure of centrality for which of the following variables?

$($a$)$ the weight of a semiconductor in grams $($measured to $7$ decimal places$)$

$($b$)$ the names of each university in the U$.$S$.($values include University of Illinois, Harvard, etc.$)$

$($c$)$ the annual revenue of a Fortune $500$ company $($over $$1$ billion, measured to $$1)$

$($d$)$ number of players on the football field for any one play $($almost always $22,$ but can be $20,21,$ or $23)$