In the Collection, go to 'Sharing'.
Click on 'Variables'. The full list of questions will open up.
Select a question by clicking on it.
Multiple questions can be selected with 'Ctrl'. Select one question, press 'Ctrl', click on the second question, and so on.
Click on 'Share', to share only the selected questions with the added users.
A pop-up will appear to confirm the sharing status. Click on 'OK' to confirm.