for exercise 还是exercising?

One day, Dad asked me to go out for a walk. "No, I have to write a book report tonight, " I coldly refused. "Come on. Just a few minutes for ________." "No, I’ve told you I have no time！" I shouted. He seemed disappointed.……

老师，这里填名词还是动名词? 都可以填吗？谢谢！

表示目的时，用 for sth. 或者用不定式 to do...，防止用 for doing ...。

所以，用 for exercise。又如：

Today many people use it for exercise. 

今天很多人用它来训练身体。