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".
We need to find the main problem. "Temel sorunu bulmak zorundayız."
What is adifferenc between " you have to " and " you must " .my answer was , you must find ...... and that was marked not correct .i want to know the difference ,if possible please .
The Turkish question gives you a clue:
Temel (adjective) "basic."
Bulmak "to find."
Zorun "the challenge."
Zorun + -da + (y) + -ız 2nd person plural suffix.
Zorundayız "we have to."
Zorundayım "I have to."
You have to find the main problem. Temel sorunu bulmak zorundayım.
The -ım suffix is 1st person singular.
My explanation is not 100% but may help you understand why Duo declined your answer.
We need a second opinion with fresh eyes.