jquery迭代~求教！解决方法

$('.o12').slideDown(1000,function(){

            $('.o11').slideDown(1000, function(){

               $('.o10').slideDown(1000, function(){

                  $('.o9').slideDown(1000, function(){

                     $('.o8').slideDown(1000, function(){

                        $('.o7').slideDown(1000, function(){

                           $('.o6').slideDown(1000, function(){

                              $('.o5').slideDown(1000, function(){

                                 $('.o4').slideDown(1000, function(){

                                    $('.o3').slideDown(1000, function(){

                                       $('.o2').slideDown(1000, function(){

                                          $('.o1').slideDown(1000);

                                          })

                                       })

                                    })

                                 })

                              })

                           })

                        })

                     })

                  })