populate a combobox with values of selected checkboxes on a previous form?

I have a form which contain a set of checkboxes. What I want to do, is when the user select some checkboxes and then click on a button, a new form will appear which contain a combobox that holds the values/texts of previously selected checkboxes.

In the above form, here what happens when the user clicks next :

private void btnNext_Click(object sender, EventArgs e)
    {
        Step3 stp3 = new Step3();

        foreach (Control c in this.Controls) {
            if (c is CheckBox) {
                stp3.addChosenModule(c.Text);
            }
        }

        stp3.Show();
        this.Hide();
    } 

And here what the form named Step3 contains in it's class:

 public partial class Step3 : Form
{
    public List<string> chosenModules = new List<string>();
    public void addChosenModule(string moduleName) {
        chosenModules.Add(moduleName);
    }

    public Step3()
    {
        InitializeComponent();
    }

    private void Step3_Load(object sender, EventArgs e)
    {
        foreach (string itm in chosenModules) {
        cbModules.Items.Add(itm);
        }
    }
}

Now, after clicking on Next, the new form shows up but the combobox is still empty ?