$(document).ready(function(){

$("select").change(function () {
  $("select option:selected").each(function () {
    var val = $(this).val()
    if(val == 0){
      $("#block1").fadeIn("slow");
      $("#block2").fadeIn("slow");
      $("#block3").fadeIn("slow");
    }if(val == 1){
      $("#block1").fadeIn("slow");
      $("#block2").hide();
      $("#block3").hide();
    }if(val == 2){
      $("#block1").hide();
      $("#block2").fadeIn("slow");
      $("#block3").hide();
    }if(val == 3){
      $("#block1").hide();
      $("#block2").hide();
      $("#block3").fadeIn("slow");
    }
        });
     }).trigger('change');
  });