填空题
以下程序段的作用是计算数据的和，数据的个数是可变的。请填空。
Private Sub Command1_Click()
Dim a As Integer
a=0
Sum a, 1, 5, 2
Print "sum of 3 = "; a
a = 0
Call Sum(a, 1, 3, 5, 7, 9)
Print "sum of 5 = "; a
End Sub
Private Sub Sum(x As integer,{{U}} 【3】 {{/U}}
Dim y As Variant
For{{U}} 【4】 {{/U}}
x = x + y
Next y
End Sub