How to preset source in RSI indicator for a cBots, without manually setting?

Hello,

I have below testing code, it will return last 1st bar's RSI values based on Open/Close/High/Low price. 

Now I want to preset sources for all the dataseries, but obviously I can't put string "Open" to replace Source_O, (in the highlighted area). What should I do to simplify the parameter setting area, to put all parameters preset in the coding stage rather than leave them for manually set?

Thank you again,

Lei

using System;
using System.Linq;
using cAlgo.API;
using cAlgo.API.Indicators;
using cAlgo.API.Internals;
using cAlgo.Indicators;

namespace cAlgo
{
    [Robot(TimeZone = TimeZones.UTC, AccessRights = AccessRights.None)]
    public class TestingRSI : Robot
    {
        [Parameter("Source Open",  Group = "RSI")] public DataSeries Source_O { get; set; }
        [Parameter("Source Close", Group = "RSI")] public DataSeries Source_C { get; set; }
        [Parameter("Source High",  Group = "RSI")] public DataSeries Source_H { get; set; }
        [Parameter("Source Low",   Group = "RSI")] public DataSeries Source_L { get; set; }

        [Parameter("Periods", Group = "RSI", DefaultValue = 14)] 
        public int Periods { get; set; }

        private RelativeStrengthIndex rsi_O;
        private RelativeStrengthIndex rsi_C;
        private RelativeStrengthIndex rsi_H;
        private RelativeStrengthIndex rsi_L;

        protected override void OnStart()
        {
            rsi_O = Indicators.RelativeStrengthIndex(Source_O, Periods);
            rsi_C = Indicators.RelativeStrengthIndex(Source_C, Periods);
            rsi_H = Indicators.RelativeStrengthIndex(Source_H, Periods);
            rsi_L = Indicators.RelativeStrengthIndex(Source_L, Periods);            
        }

        protected override void OnBar()
        {   
            Print("rsi_O.Result.Last(1) : {0}", rsi_O.Result.Last(1));
            Print("rsi_L.Result.Last(1) : {0}", rsi_L.Result.Last(1));
            Print("rsi_H.Result.Last(1) : {0}", rsi_H.Result.Last(1));
            Print("rsi_C.Result.Last(1) : {0}", rsi_C.Result.Last(1));
        }
    }
}