How to use "Interface" correctly?

I wanna to use multiple inheritance and I got to know Interface might give me help, so I create the following coding

namespace IT.Machine
{
    interface IMachine: IMachineA, IMachineB, IMachineC
    {
        public int MachineID { get; set; }
        public int CategoryID { get; set; }
    }
}

namespace IT.Machine
{
    interface IMachineA
    {
        public int ID { get; set; }
        public string A01 { get; set; }
        public string A02 { get; set; }
        public string A03 { get; set; }
    }
}

namespace IT.Machine
{
    interface IMachineB
    {
        public int ID { get; set; }
        public string B01 { get; set; }
        public string B02 { get; set; }
        public string B03 { get; set; }
    }
}

namespace IT.Machine
{
    interface IMachineC
    {
        public int ID { get; set; }
        public string C01 { get; set; }
        public string C02 { get; set; }
        public string C03 { get; set; }
    }
}

private void btnTesting_Click(object sender, EventArgs e)
{

        Machine.IMachine machine = new Machine.IMachine();
        machine.A01 = "string for A01";
        machine.A02 = "string for A02";
        machine.B01 = "string for B01";
        machine.C03 = "string for C03";
        machine.CategoryID = 9999;
        machine.MachineID = 123;
}

However, I got errors, for example...The modifier 'public' is not valid for this item in every "public".  May I know how I can fix this error?  Please advice the correct way to use "Interface" in this situation.

Please help...