: Determining if a noun receives an action or describes the subject (e.g., Tony is my friend where "friend" is a complement). Grammar Space 1 Teacher's Guide | PDF - Scribd

The answer key is more than just a list of correct letters; it is a diagnostic tool. In grammar, an answer is usually right or wrong—there is very little middle ground. Therefore, having the answer key allows for immediate correction, which is crucial for preventing the fossilization of errors.