c#程序不断询问用户输入问题不止一次

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
enter code here`namespace fuel_consumption {
class Program {
    // Program Reset & exit method at the end of program
    static bool DoItAgain()
    {
        bool startAgain = true;
        string reply = "";
        Console.Write("Start Over? (Y or N):  ");
        reply = Console.ReadLine();
        reply = reply.ToUpper();
        if (reply != "Y") 
        {
            startAgain = false;
        }
        return startAgain;
    }//End DoItAgain method
   //Startup Screen method
    static void WelcomeMessage() {
        Console.WriteLine("'n'n'tWelcome to the Fuel Consumption Calculator'n'n't");
    }// End startup Screen method
    //Begin user input method for Number of Litres
    static int InputLitres() {
        string userInput = "";
        int selection = 0;
        int minLitres = 20;
        bool inValid = true;
        //User Input Message
        while (inValid) {
            Console.Write("'nEnter the amount of litres consumed:  ");

程序一遍又一遍地问这个问题，实际上大约问了5次。

            userInput = Console.ReadLine();
            if (int.TryParse(userInput, out selection))
                if (selection < minLitres) {
                    // Deliver Error Message to User
                    Console.Write("'nPlease Enter an amount 20 litres or above'n'n Please Try Again:'n");
                }
                else {
                    inValid = false;
                }
        }
        //return the value entered by the user
        return selection;
    }//end InputLitres
    //Begin InputKM method
    static int InputKM() {
        //set user input varibles
        string userInput = "";
        int selection = 0;
        int inputLitres = InputLitres();
        int minKms = 8 * inputLitres;
        bool inValid = true;
        while (inValid) {
            Console.Write("'nEnter Kilometres Travelled: ");

然后它也会问这个问题几次

            userInput = Console.ReadLine();
            if (int.TryParse(userInput, out selection))
                if (selection < minKms) {
                    //Deliver Error Message to user and redirect back to user input of kms
                    Console.WriteLine("'n Minimum Kms is {0:f2} Kilometres, Please Enter a value of {0:f2} or higher", minKms);
                }
                else {
                    inValid = false;
                }
        }
        //return the KM Value
        return selection;
    }//End Input Kms
    static double consumptionCalculation() {
        int litres;
        int kms;
        double litresFormula;
        double formulaResult;

        //Define Base Varibles
        formulaResult = 0.0;
        litresFormula = 0.0;
        litres = InputLitres();
        kms = InputKM();
        //Calculate fuel consumption in litres per 100km
        litresFormula = (double)litres * 100;
        formulaResult = (double)litresFormula / kms;
        {
            //Return the result value
            return formulaResult;
        }
    }
    //Print results method
    static void PrintResults() {
        double kmResult = consumptionCalculation();
        Console.WriteLine("'n'n'tYour Fuel Consumption is {0} Litres per 100 Kilometres", kmResult);
    }
    //Start Program Loop Method
    static void ProgramLoop() {
        bool startAgain = true;
        //Loop through each user Input Method

        InputLitres();
        InputKM();
        consumptionCalculation();
        PrintResults();

        startAgain = DoItAgain();
    }

    static void Main(string[] args) {

        WelcomeMessage();
        ProgramLoop();
    }
}

}

谁能给我一个主意，我哪里错了?我只需要它问一次这些问题，返回值。请让它简单，因为我是新的。由于