Model answer should only be disabled for the questions within the assessment article a-15 (in page co-15). You can change this behaviour from the assessment configuration applied to a-15 in articles.json. It should be pretty obvious but have a look at the README for the assessment extension if you need.
The questions within page co-10 should all have model answer enabled.
The reset button is disabled for all questions because they are all set to have 1 attempt. Increasing the number of attempts for any question will cause the reset button to enable for that question.