1．He headed the ball into an open ________ (球门)．
答案：goal
2．The theory seems to have no ________ (根据) in fact.
答案：basis
3．Physical activity is an important ________ (因素) in maintaining fitness.
答案：factor
4．This indicates that there is a certain way quantity is ________ (代表) in their brains.
答案：represented
