<?php

$pages = array(
  "buy1.html",
  "buy2.html"
);

if (!isset($_COOKIE['bpm_buy'])){
    $n = count($pages);
    $go = rand(1,$n);
    setcookie("bpm_buy", $go, time()+60*60*24*7);
}else{
    $go = $_COOKIE['bpm_buy'];
}

header('Location: '. $pages[$go-1]);

?>

/////////////// 	I NEED TO PASS  QUERY STRING TO  THE REDIRECT.  THIS IS
////////////////	NOT WORKING: header('Location: '. $pages[$go-1]) . $_SERVER['QUERY_STRING']);