$\backslash$table$[[$Motorola Droid XYboard,$530,$Android,$10\mathrm{.}1],[$Samsung Ativ Smart PC$,590,$Windows,$11\mathrm{.}6],[$Samsung Galaxy Tab,$525,$Android,$10\mathrm{.}1],[$Sony Tablet S$,360,$Android,$9\mathrm{.}4]]$

$($a$)$ How many elements are in this data set?

$($b$)$ How many variables are in this data set?

$($c$)$ Which variables are categorical? $($Select all that apply.$)$

cost

operating system

display size

battery life

cpu manuafacturer