下面程序： PrivateSubForm_Click0 Dim x ,y，z AS Integer x=5 y=7 z=0 call PI(x ,y，z) Print Str(z) End Sub Sub Pl (By Val．a As Integer ,By Val b As Integer ,c As Integer) c= a + b End Sub 运行后的输出结果为______. A) 0 B) 12 B) Str (z) D) 显示错误信息