Doing exercise every day is necessary for students 该用it做形式主语

Doing exercise every day is necessary for students 该用it做形式主语 It is hard for us __(exercise)every day.why? it is good for us to take exercise every day It is hard for us __(exercise)every day 改错：It is important for swimmer to exercise every day. 1.It is necessary for all of us to take exercise every morni It is important for students ______ eye exercises every day. 1、doing exercise every day is good for your health（改为同义句） I think it is necessary for us keep a d_____ every day It is necessary for us to work hard every day 同义句 Doing sports every day is good for our heath.主语是什么,为什么 sport to exercise,for a fat man,every day,it is,hard,one hour,连词成句