i need to make sure that we will know the answers before and after the stimuli and know that the same person answered them

Question

we already created 3 different copies of the questionnaire. what i meant is; we have two groups in our study each group will have a different stimuli and we need to compared the answers before and after the stimuli for both groups and compare the results of the two groups
so we need to know for example that respondent A from group 1 answered the questions before the stimulus like this and after the stimulus like that.

Answer 1

Regarding to two groups I recommend using a single questionnaire, see randomization.

For the pre- and posttest you will need two copies of the questions. One to be shown before, and one after the stimulus.