This is a pretty subtle difference. I don't think a problem would ever depend just on that difference. There's probably a bigger error in one of the answer choices that you could use.
For 'purpose verbs' like 'evaluate', 'discuss', etc., the really important things to look at aren't the subtle differences. Instead, focus on these:
- what's the 'tone'? 'Cast doubt on' implies that the author is negative towards the topic, while 'confirm' would imply that the author has a positive attitude towards it.
- is it 'strong' language, or 'weak' language? Strong verbs are ones that have very clear, specific meanings, such as 'argue' or 'prove' or 'contrast'. Weaker verbs are ones that basically just mean 'talk about', like 'discuss', 'explain', 'list', etc. If your answer choice has a 'strong' verb in it, you should be very certain that the passage actually does that thing (argues, proves, contrasts, etc.) If you only have a weak verb, you don't really need to worry about it.
That said, in my mind, 'discuss' and 'describe' are totally neutral- they just mean 'talk about something' in a very general way. You could use these for almost any passage.
To 'evaluate' something means to determine whether it's right or wrong, good or bad, etc. There's a judgment involved.
To 'explain' something means to take something that's confusing or obscure, and make it simpler or clearer for the reader by clearing up ambiguities or confusing points.