What is this Ruby Challenge asking me to do?

This is the Ruby basics course. It is very basic in that I've been programming in Java, JavaScript, C, Python, etc. and just wanted to learn about Ruby now. I can open a work-space and build a ruby script that does just what is requested in the challenge. It is the last challenge on this course. It keeps telling me "Bummer..." Here is the challenge: "In the previous challenge, we wrote a method that returned the remainder of two arguments when divided. That's cool, but it would be nicer if the method returned the remainder in a nice full sentence. Use string interpolation to return the remainder inside the sentence “The remainder of a divided by b is c.” where a is your “a” variable, b is your “b” variable, and c is the value of a % b."

I found a few ways to make this work. None of those ways is acceptable, though.
I first set c = a % b and that gives me all the variables. I realized that the challenge wanted me to return the sentence with the variables. That seems simple enough. I discovered you can even do return puts "The remainder of #{a} divided by #{b} is #{c}." Or I could start the sentence with a puts on the first line after calculating c and then return c. That could be tested and shown to work with ruby puts method.rb and it works fine. So, what's the challenge asking that I don't understand? Thanks, Bruce

def mod(a, b)
  #write your code here
end