ActiveX ComboBox Duplicating Values

Hi!

I am trying to develop a 2 ComboBox's with the same drop down information, but the "drop-downs" duplicate each time I click on a selection. Do you have any recommendations for how I can fix? Additionally, any suggestions on how to use this ComboBox selection to populate a range of data (additional worksheets within same workbook) to create a comparison of data? Thank you in advance.

Private Sub ComboBox1_Change()
    'Add list entries to ComboBox1.'
    ComboBox1.AddItem "A"
    ComboBox1.AddItem "B"
    ComboBox1.AddItem "C"
    ComboBox1.AddItem "D"

    'Use drop-down list
    ComboBox1.Style = fmStyleDropDownList
End Sub

Thanks