单选题 有如下程序：
Function F(a As Integer)
b = 0
Static C
b = b + 1
c = c + 2
F = a + b + c
End Function
Private Sub Command1_Click()
Dim a As Integer
a = 2
For i=1 To 3
Print F(a)；
Next i
End Sub
运行上面的程序，单击两次命令按钮，在窗体上输出结果为
A) 4 4 4 B) 4 5 6 C) 5 7 9 D) 11 13 15