有如下函数:
Private Function firstfunc(x As Integer, y As Integer) As Integer
Dim n As Integer
Do While n ＜= 4
x=x +y
n=-+1
Loop
firstfunc = x
End Function
调用该函数的事件过程如下:
Private Sub Command1_lick()
Dim x As Integer
Dim y As Integer
Dim n As Integer
Dim z As Integer
x=1
y=1
For n = 1 To 3
z = firstfunc(x, y)
Next n
Print z
End Sub
该事件过程的执行结果是 ______。

A．1

B．3

C．16

D．9