Test questions:I got the output asked for but the answer wrong... help!

So here is the question:

Write a function named combine_sort that has two parameters named my_list1 and my_list2.

The function should combine these two lists into one new list and sort the result. Return the new sorted list.

Here is what I wrote:

my_list1 = [4, 10, 2, 5]

my_list2 = [-10, 2, 5, 10]

combine_sort = sorted(my_list1 + my_list2)

The output works.

This is the answer they wanted.

def combine_sort(my_list1, my_list2):
unsorted = my_list1 + my_list2
sortedList = sorted(unsorted)
return sortedList

#Uncomment the line below when your function is done
print(combine_sort([4, 10, 2, 5], [-10, 2, 5, 10]))

What is that? why do they want that? How am I wrong? help