Exercising every day helps you to keep in good health.为什么exe

动名词短语作主语,故要用ING形式,而exercise你为‘锻炼’是动词,动词原形是不能作主语的.
再问： 具体再举几个列子
再答： Seeing is believing .眼见为实。 Reading in bed is bad for your eyes .在床上看书对你的眼睛有害。