a button to check all test questions have been answered

Hello all,

I am creating a test for my work. I have 108 questions. Each question is in own group box and each question is either a checkbox for multiple answers, or option buttons for a,b,c,d & true/false answers.
I have done a cell link for each one to a cell beside the group box that with other formals tell the test scorer if the question was answered correct or not and adds up all the score for the whole test.

What i am looking for is a button at the end of the test that will check to see if any group boxes were not checked in any way. each answer should be checked in some sort of way.

I would also like it to have a pop up that either states something along the lines of " All answers have been completed" or "At least one answer has not been completed, please go back and check all answers". I don't need it to tell the test taker exactly which answers are missing as i think that would be over complicated. This button wont tell them if the answer is correct or not, just that they have answered something.

Any help would be grateful,
thanks,
-Nick