Enhance your photography skills — join Yellowstone’s park photographer for a hands-on program to inspire new and creative ways of enjoying the beauty and wonder of Yellowstone.

以上摘自2023年高考英语新全国卷2阅读理解A。

曾经听老师说，复合词中的名词是不用复数的，比如 a five-year-old boy，不能说成 a five-years-old boy。请问这里的 hands-on 为什么用复数 hands呢？