I'm completely lost on the use of prepositions with the present infinitive and also cui/quale (they could be used the same way; I'm not sure).
I just want to point out I know how to use these grammar points themselves, but I don't get which prepositions to place with them.
For example with questions that have to be changed to this form:
Sono in molti che hanno imparato l'italiano in questo corso.
Sono in molti _____ l'italiano in questo corso.
Here I know it's aver imparato, but I don't know how to work out the preposition!
I have a list of infinitives with prepositions in my work book, and it says imparare + a. So it should make sense that it is ad aver imparato.
But then I try to follow that logic with another verb.
The list says dimenticare + di.
So I figure that:
Ieri è stato un giorno che si dovrebbe dimenticare
= Ieri è stato un giorno di dimenticare. But the answer sheet says it's DA dimenticare.
How do you work this out?