确定.NET Framework版本的DLL

我有编译针对.NET框架和部署了一个旧的DLL。我不知道这是编译针对.NET框架的版本。我想知道我怎么能确定这个DLL编译针对.NET框架的版本？我不能相信它的来源$ C ​​$ C，因为我相信它已经升级到Visual Studio 2008，并变更为.NET Framework 3.5版。

I have an old dll that was compiled against the .NET framework and deployed. I am not sure which version of the .NET framework it was compiled against. I am wondering how I can determine which version of the .NET framework this dll was compiled against? I cannot trust the source code because I believe it has been upgraded to Visual Studio 2008 and changed to .NET framework version 3.5.