[单项选择题] 编写如下事件过程： Private sub sub1 (ByVal x1 As String, y1 As String)Dim xt As StringDim i As Intege

[单项选择题] 编写如下事件过程：

Private sub sub1 (ByVal x1 As String, y1 As String)

Dim xt As String

Dim i As Integer

i = Len(x1)

Do While i＞= 1

xt = xt + Mid(x1, i, 1)

i=i-1

Loop

y1 = xt

End Sub

Private Sub Form Click()

Dim s1 As String, s2 As String

s1= "teacher"

sub1 s1, s2

Print s2

End Sub

程序运行后，单击窗体，则窗体上显示的内容是

A．rehcaet

B．tahreee

C．themee

D．eerthea