Here is the output I am receiving, and I am having trouble of what to check for when I re examine my code for the indicated lines.

```
Traceback (most recent call last):
  File "ex27.py", line 93, in <module>
    print_first_and_last_sorted(sentence)
  File "ex27.py", line 35, in print_first_and_last_sorted
    words = sort_sentence(sentence)
  File "ex27.py", line 25, in sort_sentence
    return sort_words(words)

```

Can anyone shed some light?