为什么有些动词做主语是动词原形,有些加ing.最好弄几个例子和题目

动词本身不能作主语,要改为动名词或不定式才能作主语.如
To see is to believe.
Seeing is believing.
Reading in bed is bad for your eyes.动词原形开头是祈使句，如Open the window , please.动词原形开头是祈使句，如Open the window , please.没有可比之处，祈使句隐含主语是you( 不是动词作主语）