有三个组合框里面都是一样的代码01，02，03，如何编程实现组合框显示一个代码另外两个组合框里就自动去掉已被选择的那个代码？如下图：
         

作业？

* test.prg
CREATE CURSOR tt (f1 C(1))
INSERT INTO tt VALUES ("1")
INSERT INTO tt VALUES ("2")
INSERT INTO tt VALUES ("3")

of = CREATEOBJECT("form1")
of.show(1) 

DEFINE CLASS form1 as Form 
    ADD OBJECT combo1 as combobox WITH top=10,left=10, width=100,RowSourceType=3
    ADD OBJECT combo2 as combobox WITH top=10,left=120,width=100,RowSourceType=3
    ADD OBJECT combo3 as combobox WITH top=10,left=230,width=100,RowSourceType=3
    
    PROCEDURE Init
         = "SELECT f1 FROM tt WHERE thisform.blCombo1() INTO CURSOR tt_combo1"
         = "SELECT f1 FROM tt WHERE thisform.blCombo2() INTO CURSOR tt_combo2"
         = "SELECT f1 FROM tt WHERE thisform.blCombo3() INTO CURSOR tt_combo3"
    ENDPROC
    
    PROCEDURE combo1.InteractiveChange
         ENDPROC

    PROCEDURE combo2.InteractiveChange
         ENDPROC

    PROCEDURE combo3.InteractiveChange
         ENDPROC

    FUNCTION blCombo1()
        RETURN IIF(!EMPTY(), (f1 != ), .T.) AND ;
               IIF(!EMPTY(), (f1 != ), .T.)
    ENDFUNC

    FUNCTION blCombo2()
        RETURN IIF(!EMPTY(), (f1 != ), .T.) AND ;
               IIF(!EMPTY(), (f1 != ), .T.)
    ENDFUNC

    FUNCTION blCombo3()
        RETURN IIF(!EMPTY(), (f1 != ), .T.) AND ;
               IIF(!EMPTY(), (f1 != ), .T.)
    ENDFUNC
ENDDEFINE