Final answer:
The concept referred to is context-dependent memory, and the correct response is that it is a well-supported phenomenon. While context can aid in memory retrieval by serving as a cue, other study techniques and factors play significant roles in memory as well.
Step-by-step explanation:
Your friend's introductory psychology textbook is referring to context-dependent memory, which is the idea that recall is better if the context during testing is similar to the context during learning. This is because the environmental cues from the study context can act as retrieval cues for the memory. Therefore, your informed response would be: c) Context-dependent memory is a well-supported phenomenon.
There is a good amount of research to back up the concept of context-dependent memory, including studies showing that learning and recalling information in the same environment can facilitate memory retrieval. However, it is also true that other factors, such as the level of processing, use of elaborative rehearsal, and distributed practice, can also significantly impact memory. The idea here is that while context can help, it's not the only factor at play when it comes to efficient studying and memory recall.