a=3;b=4;

if a<b then a=0;

else a=1;

end if

Dim a(1 To 10) As Integer, f(1 To 20) As Boolean

    'f数组各元素的初值设为False，代码略

    For i = 1 To 10

       t =int(rnd()*20+1)

       If Not f(t) Then

          a(i) = t:      ⑴     

          For j = i To 2 Step -1

             If    ⑵    Then

                tmp = a(j): a(j) = a(j - 1): a(j - 1) = tmp

             End If

          Next j

       Else

               ⑶    

       End If

    Next i

上述程序中3处下划线应填入的程序代码是（  ）