var chap_array = new Array(
["GTO 6",'gto-6'],
["GTO 5",'gto-5'],
["GTO 4",'gto-4'],
["GTO 3",'gto-3'],
["GTO 2",'gto-2'],
["GTO 1",'gto-1']);

for (var i=0; i<chap_array.length; i++) {
document.getElementById('chapter_select').options[i] = new Option(chap_array[i][0],chap_array[i][1]);
}