Question about PHP $_GET ?

can certainly any1 tell tips on how to check if you have only A SINGLE $_GET changing exists…
for instance, If relating to a url like “http://localhost/index.phppage=1&para= then how will certainly program throughout PHP so that it may run particular syntax only when “page” varied exists inside url certainly not “para” & not necessarily “line”…
Plz guide me…!!

if (isset ($_GET’page’))

// web site exists.Can something
$page = $_GET’page’;
in the event that ( isset ($_GET’para’))

// these, “page” exist AND “para” is available:
$para = $_GET’para’;
// take a step with para…