Final answer:
Offering the answer key to the exam as take-home material is a mistake because it could lead to academic dishonesty, unlike the other options which support learning.
Step-by-step explanation:
The answer key to the exam would be a mistake if offered as take-home material. Providing the answer key compromises the integrity of the assessment by giving direct access to the answers, which could encourage academic dishonesty. In contrast, a detailed explanation of the concepts covered in class, additional practice problems, and a copy of the textbook are all appropriate materials. These resources support learning by reinforcing the material taught, offering additional practice, and serving as a reference.