Hola,diana,el codigo seria asi:
Código:
Private Sub UserForm_Initialize()
Dim c As ComboBox
For Each c In Me.Controls
c.AddItem "Anual"
c.AddItem "Semestral"
c.AddItem "Bimestral"
c.AddItem "Trimestral"
c.AddItem "Cuatrimestral"
c.AddItem "Mensual"
Next
End Sub
saludos.