In this context looking at is correct. ‘Apart from’ should be followed by ‘and’ not ‘but.’ ‘As stressful’ must show some kind of comparison. Here there is no comparison, hence, ‘so stressful’ is acceptable ‘Neither . . . nor . . .’ are co-ordinating conjunctions therefore one cannot be used without the other. Hence ‘or’ is suitable. In sentence D a contrast is shown, hence ‘but’ is more suitable.