GMAT Sentence Correction (SC) | The three political parties that make up the Australian coalition

i have a doubt here.

here we are talking about the coalition party, not the three parties and verb should be singular .

i think correct option should be one among D or E.

I agree with people thinking that the subject should be singular - the coalition.

It doesn't make sense three parties including another one as does the coalition including another one.

Any additional thoughts on this one?