迭代VB.Net中的二维数组

Dim test2DArr As String(,) = {{"A","B"},{"C","D"}}

For Each s As String In test2DArr
  MsgBox(s)
Next

运行时,弹出四个消息框,显示“A”,“B”,“C”,然后“D”.

换句话说,它具有与以下完全相同的行为：

Dim test1DArr As String() = {"A","B","C","D"}

For Each s As String In test1DArr
  MsgBox(s)
Next

有人可以解释这个“功能”吗？我需要在这里施加一些显然不受支持的结构.上面的第一个代码示例应该是：

Dim test2DArr As String(,"D"}}

For Each arr As String(,) In test2DArr
  MsgBox(arr(0) & "," & arr(1))
Next

并且应该产生两个消息框：“A,B”和“C,D”,但是编译器坚持认为迭代2-d数组会产生一个字符串序列,而不是一串字符串数组.

我做错了什么,或者.Net的2-D阵列实现真的很脆弱？