单项选择题

在窗体上画一个命令按钮(名称为Command1),并编写下列代码:   Function Fun1(ByVa1 a As Integer,b As Integer)As Integer    Dim t As Integer    t=a-b    b=t+a    Fun1=t+b   End Function   Private Sub Command1Click()   Dim X As Integer   x=10   Print Fun1(Vun1(X,(Fun1(x,x-1))),x-1)   End Sub   程序运行后,单击命令按钮,输出结果是( )。

A.10
B.0
C.11
D.21