This is a recurring question.
Soru = question -- Sorun = your question -- Sorunu = your question (object form)
Sorun = problem -- Sorunu = the problem (object form).
You can write: "We have to find the basic problem" OR "We have to find your basic question".
You cannot write: "the basic question" which would be: "temel soruyu";
nor can you write "your basic problem" which would be: "temel sorununu".
One of the tricky parts of Tk, you can't tell suffix from root word unless you know the root word. This is not generally true in Indo-European languages, where the suffix is clear even if it's on a nonsense word.
"Temel soru" (Basic question) --> "Temel soruyu" (the basic question [accusative])
"Temel sorusu" (His/Her/Its basic question)
Ahh. I see. I thought it was a compound noun. Similarly, I also thought "temel sorunu" was a compound noun. Haha.
What is the difference between 'temel,' 'ana,' and 'baş'? It did not accept 'ana'