Clear Contents Of List Box

Hey guys,

I have created a list box that is based on a select statement using the value of another list box.

for example:
box1 lets you select aaaa
box2 shows a list of all the records that have aaaa

now I need to know how to clear the list as box1 is changed

right now it will give me

aaaa123
aaaa789
bbbb123
bbbb789

I need to know how to clear it so that
aaaa is deleted and bbbb shows when the code is stepped through a second time.

code is as follows:

Private Sub Car_Empty_GotFocus()

prefix_input = Form_Car_Loading.Prefix.Value
Set db = DBEngine.OpenDatabase blah, blah, blah
sqlstatement = "SELECT [prefix], [Car_number], [Date_loaded] " & _
" FROM Car_loading where isnull(Date_Loaded)= true and prefix= '" & prefix_input & "' "
Set record = db.OpenRecordset(sqlstatement, dbOpenSnapshot, dbSeeChanges)
Move first
Do Until record.EOF = True
Form_Car_Loading.Car_Empty.AddItem (record(0) & record(1))
record.MoveNext
Loop

db.Close
End Sub