如何在谷歌条形图中绘制一条横跨条形图的平均线？

// 引入谷歌图表库
google.charts.load('current', {'packages':['corechart']});
google.charts.setOnLoadCallback(drawChart);

function drawChart() {
  // 准备数据集
  var data = google.visualization.arrayToDataTable([
    ['类别', '数值'],
    ['类别1', 100],
    ['类别2', 200],
    ['类别3', 150],
    ['类别4', 300]
  ]);

  // 计算平均值
  var average = 0;
  var numRows = data.getNumberOfRows();
  for (var i = 0; i < numRows; i++) {
    average += data.getValue(i, 1);
  }
  average /= numRows;

  // 创建图表对象
  var chart = new google.visualization.BarChart(document.getElementById('chart_div'));

  // 设置图表选项
  var options = {
    annotations: {
      textStyle: {
        fontSize: 12,
        color: 'black'
      },
      stem: {
        color: 'transparent'
      },
      style: 'line'
    }
  };

  // 绘制图表
  chart.draw(data, options);

  // 添加平均线
  var averageLine = chart.createAnnotation();
  averageLine.setProperties({
    type: 'line',
    xValue: 0,
    yValue: average,
    x2Value: numRows - 1,
    y2Value: average,
    lineWidth: 1,
    color: 'red'
  });
  chart.draw(data, options);
}