I really assume that if your teacher is asking you this and you are in 10th grade that there is a specific answer that you are expected to get out of your book.  You should look because different books have different answers...

My answer to this would be that China did not want to be a junior partner or a "little brother" to the Soviet Union.  The two countries were both communist, but that did not mean that they agreed on everything.  For example, China had a war with India in the early 1960s and the Soviets did not back them because they wanted a good relationship with India.

So the reason for the disputes, to me, is that these were two countries that did not agree on some important things and who shared a long border.   It seems natural that disputes would arise, especially since China was worried about being pushed around by the Soviets.