（加试题） 有如下VB程序段：

Dim a(1 To 10) As Integer

Dim s As String, n, i As Integer

s = "54851845236": n = Len(s)

For i = 1 To n - 1

a(i) = Val(Mid(s, i, 2))

Next i

For i = 1 To n - 2

k = i

For j = i + 1 To n - 1

If a(k) < a(j) Then k = j

Next

If k <> i Then

t = a(k): a(k) = a(i): a(i) = t

End If

Next i

Text1.Text = Str(a(1))

该程序段运行后，文本框 Text1 中显示的内容是：（  ）

A、18

B、54

C、85

D、8