It is a quesiton in the quiz , for everyone else here is the code example:

$myArray = array("January" => "Winter", "February" => "Winter", 
"March" => "Spring", "April", "May" => "Spring", "June" => "Summer", 
"July" => "Summer", "August" => "Summer", "September" => "Fall", 
"October" => "Fall", "November" => "Fall", "December" => "Winter"); 

What is the key of the fourth element of the array ?

I'll explain from here, I can understand your confusion but Treehouse threw a really clever question, if you think that the array contains only pairs of Keys => Values, then it would look like the array has two keys on the fourth element. But remember that an array can contain different types of data, even objects. In this case the fourth element in the array is just the string "April" , hence the value of it's key is zero. Hope this is clear enough. Good luck , keep coding.