In the 'EDIT' – 'Questionnaire' tab, you can set the respondent to see the answer they have already selected when the question is displayed, but can otherwise change it.
For the 'Categories - Single answer', 'Categories - Multiple answers' and 'Table - Single answer' question types, open the question settings and in the 'Advanced' tab, select the default answer for the respondents from the drop-down list under 'Preset value'.
The functionality is particularly useful for different forms and sign-ups, where you assume that the majority will select the same answer (e.g. 'Yes, I confirm my participation').