Can I rewrite this?

[Anonymous]

Hello :)

I'd like to ask about rewriting of the sentence using infinitives to one using clause.

Some sentences like #1 can be changed the sentences using that-clause like #2.
How about #3? Can I change #3 to #4? Do you use #4?

#1 It is necessary for us to learn English.
#2 It is necessary that we learn English.

#3 It is difficult to explain what happened.
#4 It is difficult that we explain what happened.

Would you help me understand this?

With regards
Lina

[Tdol]

We don't use #4.