上溯造型到一个泛型类型

我有以下的类层次：

class A {
 /// stuff
}

class B : A {
 /// stuff
}

class C<T> : B {
  /// stuff
}

然后某处完全不同的我有以下三种方法：

Then somewhere completely different I have the following three methods:

public void foo(A a) {
}

// overload 1
public void bar(B b) {
}

// overload 2
public void bar<T>(C<T> ct) {
}

现在，不管是什么原因，我需要调用正确的从foo条中给出的实际类型A.也就是说，如果A实际上是B型的，我需要调用超负荷1，如果A实际上是C型（无论T可），我需要调用超负荷2.与的完整性，如果A不是b或C，什么也不做。

Now, for whatever reason, I need to call the "right" bar from foo given the actual type of A. That is, if A is actually of type B, I need to call overload 1 and if A is actually of type C (whatever T may be), I need to call overload 2. And for completeness, if A is not either B or C, do nothing.

现在，我使用的是Type类的IsAssignableFrom方法来决定是否上转换到b是可能的：

Right now, I am using the IsAssignableFrom method of the Type class to decide if the upconversion to B is possible:

public void foo(A a) {
   if (typeof(B).IsAssignableFrom(a)) {
      bar((B)a);
   }
}

不过，这需要在C变种为好。所以，问题是，我怎么执行这个向上转型？反射？动力学？我们使用在C＃5，我不能使用。

But this takes in the C variants as well. So the question is, how do I perform this upcast? Reflection? dynamics? We are using .NET 4, so anything that was introduced in C# 5, I cannot use.