Answer:
D) Keep a record of Cristal's results and modify the plan if necessary.
Step-by-step explanation:
This is the best strategy that Crystal's teacher can follow. In this example, Crystal's teacher is now following a strategy that has a clear goal and that appears promising when it comes to Cristal's performance. However, in order to ensure that this is the case, the teacher should keep track of Cristal's results. If at some point the strategy appears to be uneffective, then she can modify the plan.