Questions are locked when the question has already collected responses. This means that you cannot add, remove, or re-order answer options.
Why do you lock the questions?
The questions are locked so that the data which has already been collected cannot be damaged.
Is it safe to make other changes to the question?
Any changes the survey builder will allow you to make are safe. However, if you were to move your answer options arround by changing the text the correct responses would no longer be attached to the answer options.
What happens when I use the 'delete all responses for this question' feature?
When deleting the responses for the question this will delete all of the answers associated to this question. This will not affect answers to other questions which have been collected.
I have deleted the answers for my question, can I get them back?
Once you have deleted the answers it is not possible to get them back.