The correct option is
D they had a quarrel
In order to answer the given question, let's read the passage. We can understand that the lion wanted to catch the bulls, but could never catch them as they were always united. But one day the bulls had a fight and they didn't speak to each other, and they went to different areas to graze. Hence, we can say that the bulls went in different directions because they had a fight.
Option A - They didn't want to see new pastures, they wanted to avoid talking to each other as they had had a fight. Hence, option A is incorrect.
Option B - The bulls did not want to search green grass. That's not the reason why the bulls went in different directions. Hence, option B is incorrect.
Option C - Yes, the bulls had a fight. 'Fight' and 'quarrel' are synonyms. As they had a fight, they went in different directions. Hence, option C is correct.
Option D - It is an incorrect choice as option A and B are incorrect, and option C is the answer.