Multiple choice general knowledge Which is correct..? He is making a big mistake. He is making a great mistake. a&b none Reveal answer Fill a bubble to check yourself A Correct answer Explanation The standard idiomatic expression is 'a big mistake'. While 'great' can mean large in some contexts, in the fixed expression 'make a mistake', we use 'big' as the modifier. 'A great mistake' is not standard English usage in this context.