Please notice that the grader does give you a very specific message about what is wrong: it looks like you must have modified the code in that cell and removed the comment line that included the tag UNQ_C1. There was no reason to do that and it was a mistake, as we see from the result. As a general matter, it is recommended to only change things in the “YOUR CODE HERE” areas. It’s not illegal to change or add code outside those boundaries, but you need to be sure you know what you are doing if you “go there”. 
You can recover what the template code needs to look like by getting a fresh copy of the notebook using these instructions.