如果单纯的使用要加的，句子中没有其他成分，即：watching tv， cleaning room！都是
名词短语。
以下或许可以让你明白！只有加上ing才可以算的上
名词性短语ing短语练习注意要点
1，要注意它与主句主语有逻辑主谓关系。如：Seeing the teacher,her face turned red."her face"与"seeing"就没有逻辑主谓关系，就是错句。应说：Seeing the teacher, she turned red.
2，要注意它没有连词这一特点。Coming to our school,you'll see a beautiful tall building.
3，要注意
及物动词的-ing后要带宾语，带双宾的-ing后要带双宾，不及物的-ing后不能有宾语。如：Knowing something is one thing,telling somebody something is another thing.
Living,I'll never stop studying.
4，要注意动作发生在前，又是主句的原因或条件的-ing短语要用
完成时Hxdying done...如
Hxdying seen the film,I couldn't sleep.
Hxdying filled the form,you'll get a number.
5,要注意否定的-ing:要把not放在-ing短语前。如 Not hxdying money,I can't buy a cup of coffee. Not hxdying had breakfast ,I am very hungry.
参考资料：http://yy.china-b.com/hdyy/523622.html