Which TWO of the following statements are true of blocking? 1: The phenomenon of blocking provides an interesting and much-studied instance of failure to learn, in spite of contiguous presentations of the CS and the US 2: In a blocking experiment, animals receive training with what is termed a compound CS (Phase 2) 3: The experimental group has first received a phase of training in which the US alone is conditioned (Phase 1) 4: The experimental groups shows no (or very little evidence of learning about the CS that is presented in Phase 1