请以json形式给出北京、上海和广州三个城市的面积和人口数据，每座城市的数据必须包含面积和人口，城市名称必须中英文对照并包含城市缩写。
user
```json
{
  "cities": [
    {
      "name_cn": "北京",
      "name_en": "Beijing",
      "short_name": "BJ",
      "area": "16,410.54平方公里",
      "population": "21,540,000人"
    },
    {
      "name_cn": "上海",
      "name_en": "Shanghai",
      "short_name": "SH",
      "area": "6,340.5平方公里",
      "population": "24,281,400人"
    },
    {
      "name_cn": "广州",
      "name_en": "Guangzhou",
      "short_name": "GZ",
      "area": "7,434.4平方公里",
      "population": "15,305,922人"
    }
  ]
}
```
assistant