var preloaded = [];

		for (var i = 1; i <= 7; i++) {
			preloaded[i] = [loadImage(i + "_0.jpg"), loadImage(i + "_1.jpg")];		//设置图片的OnMouseOver和OnMouseOut的路径
		}

		function init() {

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

				menu1.onactivate = function() { swapImage("title1", preloaded[1][1].src) };
				menu1.ondeactivate = function() { swapImage("title1", preloaded[1][0].src) };

                //menu2.onactivate = function() { swapImage("title2", preloaded[2][1].src) };
				//menu2.ondeactivate = function() { swapImage("title2", preloaded[2][0].src) };

				menu4.onactivate = function() { swapImage("title4", preloaded[4][1].src) };
				menu4.ondeactivate = function() { swapImage("title4", preloaded[4][0].src) };

			}
		}

		function loadImage(sFilename) {
			var img = new Image();
			img.src ="images/title_" + sFilename;
			return img;
		}

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