Multiple choice question in Storyline 360

Hi,

I add a "multiple choice question" slide in my course on storyline 360. 

For this question, he offers 4 answer choices. I added a 5th answer which is the correct answer.

When I do the test, if I choose one of the first 4 answers it automatically erases the previous answer (that's good).

Unfortunaltely, On the other hand, if I choose answer 5 and I had already clicked on answer 1,2,3 or 4 before, they remain selected. Therefore, the answer is false because 2 answers remain checked.

How do I get my 5th answer into the quiz without this error?

Thanks for your help.

Karen