查了下字典,发现表不再有兴趣的时候不要复数,表利益,多种兴趣的时候需要加.
如下：
1.兴趣; 爱好,嗜好
He lost interest in much of his research.
他对大部分研究工作失去了兴趣.
His two interests in life are music and paintings.
他生平两大爱好是音乐和绘画.
2.利益
One should not look after one's own interests alone.
一个人不应当只顾自己的利益.
所以应该是I have no interest in sports.