I'm leaving the present situation just because of expiry of my employment contract. 我离开现职是因为工作合同期满了。

　　Why have you changed your job so frequently? 你为什么换工作这么频繁？

　　I didn't enjoy the work very much because there was not much for me to do at my post. 我不是很喜欢那份工作，因为我在那个职位上没多少事情可干。