il avait beaucoup de mal à choisir le pays

Question

Why can't we use "vraiment" here for "really"? and why does it contract to "de" ? I know its because of the quantity of "beaucoup" however the expression is "avoir du mal à"?

Chris Wirt · Accepted Answer

Sure, use vraiment or beaucoup, it's the difference between "really" and "a lot". You're level C1 so you know how these writing exercises work and what self-grading means, right?
Regarding the other question: avoir du mal has a partitive article ("to have some difficulty"). If you want to say "a lot of difficulty" you use avoir beaucoup de mal. It isn't a fixed phrase in this respect.