填空题
下面的程序是找出两个正整数a和b，使得a＜b、a+ b=99、a和b的最大公约数是3的倍数，并统计满足条件数对的个数。
Option Explicit
Dim a As Integer, b As Integer, n As Integer, c As Integer
Private Function Gcd (ByVal a As Integer, Byval b As Integer) As Integer
do
c=a Mod b: a=b=c
Loop
__ 1__
Gcd=a
End Function
Private Sub form_ Click()
n=0
for a= 1 To 49
b=
__ 2__
c= Gcd (a, b)
if c Mod 3= 0 then
__ 3__
Print a, b, c
End if
Next a
Print n
End Sub