a chanllenge to后加要挑战的事情,为动词形式,如a chanllenge to climb the tree a challenge of也是加挑战的事,为名词形式,如a challenge of tree climbing a challenge for后面加人,为对某人而说是挑战,如a challenge for me
a chanllenge to后加要挑战的事情,为动词形式,如a chanllenge to climb the tree a challenge of也是加挑战的事,为名词形式,如a challenge of tree climbing a challenge for后面加人,为对某人而说是挑战,如a challenge for me