单选题
下面程序的功能是找出这样一个三位整数：它等于每位数字的阶乘之和，例如145就是这样的数（即145 = 1！+ 4！+ 5！）
Private Sub Command1_Click()
Dim x As Integer, i As Integer, j As Integer, k As Integer
For i = 1 To 9
For j = 0 To 9
For k = 0 To 9
a = ___________________
If a = fact(i) + fact(j) + fact(k) Then
Print a
End If
Next k
Next j
Next i
End Sub
Function fact(n As Integer) As Long
Dim x As Long
x = 1
For k = 1 To n
x = x * k
Next k
fact = x
End Function
程序不完整，在横线上应填写的是