主题：求助！在窗口中加载下拉列表

在窗口 afterload中 建了三个combobox
Dim cb1 As WinForm.ComboBox = e.Form.Controls("ComboBox1")
Dim cb2 As WinForm.ComboBox = e.Form.Controls("ComboBox2")
Dim cb3 As WinForm.ComboBox = e.Form.Controls("ComboBox3")
cb1.ComboList = DataTables("表A").GetComboListString("第一列")

求助。。请问 cd2 怎么调取对应cd1的列表
                 cd3怎么调取对应cd1 cd2的列表