---

private void comboBoxFigure_SelectedIndexChanged(object sender, EventArgs e)
{
    numericUpDown1.Visible = true;
    numericUpDown2.Visible = false;
    numericUpDown3.Visible = false;

    label1.Visible = true;
    label2.Visible = false;
    label4.Visible = false;

    if (comboBoxFigure.SelectedIndex == 0)
    {
        label1.Text = "Сторона";
    }
    else if (comboBoxFigure.SelectedIndex == 1)
    {
        label1.Text = "Ширина";
        label2.Text = "Высота";

        numericUpDown2.Visible = true;
        label2.Visible = true;
    }
    else if (comboBoxFigure.SelectedIndex == 2)
    {
        label1.Text = "Радиус";
    }
    else if (comboBoxFigure.SelectedIndex == 3)
    {
        label1.Text = "Сторона A";
        label2.Text = "Сторона B";
        label4.Text = "Сторона C";

        numericUpDown2.Visible = true;
        numericUpDown3.Visible = true;

        label2.Visible = true;
        label4.Visible = true;
    }
    else if (comboBoxFigure.SelectedIndex == 4)
    {
        label1.Text = "Основание A";
        label2.Text = "Основание B";
        label4.Text = "Высота";

        numericUpDown2.Visible = true;
        numericUpDown3.Visible = true;

        label2.Visible = true;
        label4.Visible = true;
    }
}