Making the answer compulsory
This option allows to make the answer to any question compulsory. As long as the respondent hasn't answered the question, he cannot continue answering the questionnaire.
In the dialog box of the definition of questions, the tab Controls, tick Mandatory response.
If it is a multiple-choice question, you can indicate the number of mandatory responses wished.
If it is a table of questions, we can make the responses mandatory for the whole table, or question after question (lines of the table).
It is not advised to make the response mandatory for all the questions. More importance must be given to this option concerning some crucial questions and filters of the questionnaire.
You can possibly take an instruction and an alert to display if no answer to the question is given by the respondent or to any line of the table.