C# Pick one of two static class at runtime

C#. Basically I had one static class A, having multiple static properties a, b, c,d... I was able to access it as usual A.a or A.b.

Now I have another static class B with same set of static properties. At the runtime based on certain condition, its need to be decided which class (A or B) need to be picked.

any idea how to achieve it.