The Interactivity Dialog is more or less interactive like the Gap page. You have to give the possible answers and the user must type one of the options. If the user gives an incorrect answer, the first possibility is shown.
So, the user is not free in his answers and the answers are not kept. The interactive dialog is an exercise.
It is not possible to control answers of the learners himself?
What you want to do could be in the Interactivity > Model Answer.
I made a small example
here
.
Ronald