求指导一个实现三级下拉框的Jquery或Ajax脚本（已有JSON数据）

[
    {
        "reports": [
            {
                "companies": [
                    {
                        "companyName": "company1"
                    }, 
                    {
                        "companyName": "company2"
                    }
                ], 
                "rptName": "rpt1"
            }, 
            {
                "companies": [
                    {
                        "companyName": "company1"
                    }, 
                    {
                        "companyName": "company2"
                    }
                ], 
                "rptName": "rpt2"
            }
        ], 
        "typeName": "type1"
    }, 
    {
        "reports": [
            {
                "companies": [
                    {
                        "companyName": "company1"
                    }, 
                    {
                        "companyName": "company2"
                    }
                ], 
                "rptName": "rpt1"
            }, 
            {
                "companies": [
                    {
                        "companyName": "company1"
                    }, 
                    {
                        "companyName": "company2"
                    }
                ], 
                "rptName": "rpt2"
            }
        ], 
        "typeName": "type2"