Please read this MSDN carefully. It says:- Top-level types, which are not nested in other types, can only have internal or public accessibility. The default accessibility for these types is internal. Nested types, which are members of other types, can have declared accessibilities as indicated in the following table.So, parent class is Internal by default.
Default access modifier for class in C# is private. Check here: http://msdn.microsoft.com/en-us/library/ba0a1yw2.aspx
internal
Public
private
Private
i hope its private as per Msdn