Doing sports is good for us

Doing sports is good for us _____ sports is good for us.前面用To do还是Doing.为什么? Doing sports does good to/for us.Doing sports does good to/f Doing sports every day is good for your health Doing more o_____ sports is good for you. Playing sports is good for us 这里为什么用playing _____morning exercises is good for us.A.Do B.Doing Doing morning exercises is good for us.（同义句） Doing morning exercises is good for us.(同义句) ____ doing moring[ ]is good for us填什么动词形式 I think sports () good for us. Doing sports is good for health.为什么用is不用are?