Long story short: I’ve basically got the following setup:

public class A : MonoBehaviour {}
 public class B : A {}
 ...
 public class C : MonoBehaviour {
 public A[] a;
 }

I’ve got an instance of C in the scene, and I can drag neither A nor B into it in the inspector. Not the biggest problem, but a little annoying (or maybe I’m just overlooking something really dumb).