Как удалить дубликаты ключей в разных combobox?

---

Я использую пару ключ-значение, чтобы сформулировать 4 разных comboBox, но один и тот же ключ будет отображаться из предыдущего comboBox в новый comboBox. Я новичок в windows form, поэтому не уверен, что это также проблема привязки источника данных.

Что я уже пробовал:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace BillCalculator
{
    public partial class Form1 : Form
    {
      

        public Form1()
        {
            InitializeComponent();

            
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            // Create a List to store our KeyValuePairs
            List<KeyValuePair<string, Decimal>> data = new List<KeyValuePair<string, Decimal>>();

            //**BEVERAGE**
            data.Add(new KeyValuePair<string, Decimal>("Soda", 1.95m));
            data.Add(new KeyValuePair<string, Decimal>("Tea", 1.50m));
            data.Add(new KeyValuePair<string, Decimal>("Coffee", 1.25m));
            data.Add(new KeyValuePair<string, Decimal>("Mineral Water", 2.95m));
            data.Add(new KeyValuePair<string, Decimal>("Juice", 2.50m));
            data.Add(new KeyValuePair<string, Decimal>("Milk", 1.50m));

            // Clear the combobox
            beverageBox.DataSource = null;
            beverageBox.Items.Clear();

            // Bind the combobox
            beverageBox.DataSource = new BindingSource(data, null);
            beverageBox.DisplayMember = "Key";
            beverageBox.ValueMember = "Value";


            //**APPETIZER**
            {
                appetizerBox.BindingContext = new BindingContext();

                data.Add(new KeyValuePair<string, Decimal>("Buffalo Wings", 5.95m));
                data.Add(new KeyValuePair<string, Decimal>("Buffalo Fingers", 6.95m));
                data.Add(new KeyValuePair<string, Decimal>("Potato Skins", 8.95m));
                data.Add(new KeyValuePair<string, Decimal>("Nachos", 8.95m));
                data.Add(new KeyValuePair<string, Decimal>("Mushroom Caps", 10.95m));
                data.Add(new KeyValuePair<string, Decimal>("Shrimp Cocktail", 12.95m));
                data.Add(new KeyValuePair<string, Decimal>("Chips and Sala", 6.96m));

                // Clear the combobox
                appetizerBox.DataSource = null;
                appetizerBox.Items.Clear();

                // Bind the combobox
                appetizerBox.DataSource = new BindingSource(data, null);
                appetizerBox.DisplayMember = "Key";
                appetizerBox.ValueMember = "Value";
            }

            //**MAIN COURSE**
            {
                mainCBox.BindingContext = new BindingContext();

                data.Add(new KeyValuePair<string, Decimal>("Chicken Alfredo", 13.95m));
                data.Add(new KeyValuePair<string, Decimal>("Chicken Picatta", 13.95m));
                data.Add(new KeyValuePair<string, Decimal>("Turkey Club", 11.95m));
                data.Add(new KeyValuePair<string, Decimal>("Lobster Pie", 19.95m));
                data.Add(new KeyValuePair<string, Decimal>("Prime Rib", 20.95m));
                data.Add(new KeyValuePair<string, Decimal>("Shrimp Scampi", 18.95m));
                data.Add(new KeyValuePair<string, Decimal>("Turkey Dinner", 13.96m));
                data.Add(new KeyValuePair<string, Decimal>("Stuffed Chicken", 14.96m));
                data.Add(new KeyValuePair<string, Decimal>("Seafood Alfredo", 15.96m));
                
                // Clear the combobox
                mainCBox.DataSource = null;
                mainCBox.Items.Clear();

                // Bind the combobox
                mainCBox.DataSource = new BindingSource(data, null);
                mainCBox.DisplayMember = "Key";
                mainCBox.ValueMember = "Value";
            }

            //**DESSERT**
            {
                dessertBox.BindingContext = new BindingContext();

                data.Add(new KeyValuePair<string, Decimal>("Apple Pie", 5.95m));
                data.Add(new KeyValuePair<string, Decimal>("Sundae", 3.95m));
                data.Add(new KeyValuePair<string, Decimal>("Carrot Cake", 5.95m));
                data.Add(new KeyValuePair<string, Decimal>("Mud Pie", 4.95m));
                data.Add(new KeyValuePair<string, Decimal>("Apple Crisp", 5.95m));
                
                // Clear the combobox
                dessertBox.DataSource = null;
                dessertBox.Items.Clear();

                // Bind the combobox
                dessertBox.DataSource = new BindingSource(data, null);
                dessertBox.DisplayMember = "Key";
                dessertBox.ValueMember = "Value";
            }
        }
        private void Appetizer_Click(object sender, EventArgs e)
        {

        }
 
  
        private void beverageBox_SelectedIndexChanged(object sender, EventArgs e)
        {
          // Get the selected item in the combobox
    KeyValuePair<string, Decimal> selectedPair = (KeyValuePair<string, Decimal>)beverageBox.SelectedItem;

            // Show selected information on screen
            lblSelectedKey.Text = selectedPair.ToString();
            
        }

        private void appetizerBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            // Get the selected item in the combobox
            KeyValuePair<string, Decimal> selectedPair = (KeyValuePair<string, Decimal>)appetizerBox.SelectedItem;

            // Show selected information on screen
            lblSelectedKey2.Text = selectedPair.ToString();
        }

        private void mainCBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            // Get the selected item in the combobox
            KeyValuePair<string, Decimal> selectedPair = (KeyValuePair<string, Decimal>)mainCBox.SelectedItem;

            // Show selected information on screen
            lblSelectedKey3.Text = selectedPair.ToString();
        }

        private void dessertBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            // Get the selected item in the combobox
            KeyValuePair<string, Decimal> selectedPair = (KeyValuePair<string, Decimal>)dessertBox.SelectedItem;

            // Show selected information on screen
            lblSelectedKey4.Text = selectedPair.ToString();
        }
    }
 }

---