var preloaded = [];

                for (var i = 1; i <= 9; i++) {
                        preloaded[i] = [loadImage(i + "-0.jpg"), loadImage(i + "-1.jpg")];
                }

                function init() {

                        if (mtDropDown.isSupported()) {
                                mtDropDown.initialize();

                                menu1.onactivate = function() { swapImage("button1", preloaded[1][1].src) };
                                menu1.ondeactivate = function() { swapImage("button1", preloaded[1][0].src) };

                                menu2.onactivate = function() { swapImage("button2", preloaded[2][1].src) };
                                menu2.ondeactivate = function() { swapImage("button2", preloaded[2][0].src) };

                                menu3.onactivate = function() { swapImage("button3", preloaded[3][1].src) };
                                menu3.ondeactivate = function() { swapImage("button3", preloaded[3][0].src) };

                                menu4.onactivate = function() { swapImage("button4", preloaded[4][1].src) };
                                menu4.ondeactivate = function() { swapImage("button4", preloaded[4][0].src) };

                                menu5.onactivate = function() { swapImage("button5", preloaded[5][1].src) };
                                menu5.ondeactivate = function() { swapImage("button5", preloaded[5][0].src) };

                                menu6.onactivate = function() { swapImage("button6", preloaded[6][1].src) };
                                menu6.ondeactivate = function() { swapImage("button6", preloaded[6][0].src) };

                                menu7.onactivate = function() { swapImage("button7", preloaded[7][1].src) };
                                menu7.ondeactivate = function() { swapImage("button7", preloaded[7][0].src) };

                                menu8.onactivate = function() { swapImage("button8", preloaded[8][1].src) };
                                menu8.ondeactivate = function() { swapImage("button8", preloaded[8][0].src) };
								
								menu9.onactivate = function() { swapImage("button9", preloaded[9][1].src) };
                                menu9.ondeactivate = function() { swapImage("button9", preloaded[9][0].src) };

                        }
                }

                function loadImage(sFilename) {
                        var img = new Image();
                        img.src ="http://www.xysjj.gov.cn/images/nav/" + sFilename;
                        return img;
                }

                function swapImage(imgName, sFilename) {
                        document.images[imgName].src = sFilename;
                }