Which one of the following qualify as rules for naming variables?

Select all that apply.

$($i$)$ Select all that apply

A may consist of letters $($upper or lower$)$; digits; and the underscore $(\_{?}_{?}$ characters.

B must begin with a letter or an underscore $($

must not be longer than $31$ characters. Although there is no rule on the length of a variable name some compilers may complain if the variable name is more than $31$ characters.

may not be a reserved word of $C($e$.$g$.$ "include" D is a reserved word$).$ Please see section $2\mathrm{.}3$ for more on reserved words.