[單項(xiàng)選擇題] 編寫如下事件過程：

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

程序運(yùn)行后，單擊窗體，則窗體上顯示的內(nèi)容是

A．rehcaet

B．tahreee

C．themee

D．eerthea

A解析：[分析]： 可以看出，Sub1(ByVal x1 As String，y1 As String)的作用是將參數(shù)x1的字符逆序處理，然后賦給y1，而y1是傳址引用的，可以直接返回處理結(jié)果。