如何绘制重叠的Google条形图

Question

下面是我为堆叠式条形图编写的代码，我希望绘制重叠的Google条形图...

---

    var options = {
    title: 'Ontology Performance',
    seriesType: 'bars', 
    hAxis: {title: 'Projects',
            titleTextStyle: {color: 'blue'}},
    vAxis: {
            /*minValue: 0,*/
      /*      scaleType: 'mirrorLog',*/
      viewWindowMode:'pretty',

      },
       isStacked:"percent" 
      // intervals: { style: 'boxes' }
      // intervals: { 'lineWidth':2, 'barWidth': 0.5, style: 'boxes' },
    };

    var chart = new google.visualization.ColumnChart(document.getElementById('onto_performance'));
    chart.draw(data,options);
    }
    </script>

有人可以帮我吗？