Final answer:
The most appropriate class interval to add to the histogram for the tallest 8 students' heights in Diego's math class is 87-89 inches (option C).
Step-by-step explanation:
The most appropriate class interval to add to the histogram for the tallest 8 students' heights in Diego's math class would be 87-89 inches (option C). Looking at the given data, we can see that the tallest students have heights ranging from 87 inches to 89 inches. Adding this class interval to the histogram will accurately represent the range of heights for the tallest students in the class.