Final answer:
The average rate at which the water level changed is 1 inch per week, calculated by dividing the total change in water level (13 inches) by the number of weeks (13).
Step-by-step explanation:
The student's question asks to find the average rate at which the water level of a lake changed during a 13-week-long dry spell. The water level fell by a total of 13 inches over the 13 weeks.
To calculate the average rate of change, we divide the total change in water level by the total number of weeks. So, the average rate of change is:
13 inches / 13 weeks = 1 inch per week
Therefore, the correct answer is: A. 1 inch per week.