Excel VBA ComboBoxes to Omit Previously Selected Options -

i have several activex comboboxes predefined list of names:

"variables!$b$1:$b$23" 

the comboboxes in cells a2 - a24. comboboxes omit selected options. example, if select "john doe" in a2 combobox, when open a3 combobox "john doe" not listed option. looking @ combobox_change option combobox code eludes me. i'm sure can see feeble attempt below:

private sub combobox1_change()  dim combovalue string  combovalue = worksheets("roster").oleobjects("combobox1").object.value  = 2 worksheets("variables").range("c1")     listvariable = worksheets("variables").range("b" & i)     if (listvariable = combovalue)     'change other comboboxes     end if next end sub