The output of the following code is:

$var $={?}^{\text{'}}\text{'}$;

$var $=($ $var $==$ true $)$;

$var $=($ $var $==$ false $)$;

$var $={?}^{\text{'}}{0}^{\text{'}}$;

$var $=($ $var $==$ true $)$;

$var $=($ $var $==$ false $)$;

echo $var;

Select one:

a$.1$

b$.$ no output

C$.$ Null

d$.0$