题目

有如下程序段： Dim a(4) As Integer Private Sub Command1_Click()Dim s As String a(1)=10:a(2)=30:a(3)=20:a(4)=40s=doit(4)Label1.Caption=s End Sub Function doit(k As Integer) As StringIf k=1 Then doit=Str(a(1)) Else doit=doit(k-1) & Str(a(k))End If End Function 程序运行后,标签Label1中显示的内容是（ ） A . 10 20 30 40 B . 10 30 20 40 C . 40 30 20 10 D . 40 20 30 10Thank you for ________ me so well.A.teachB.teachingC.to teachD.taught