He opened the door to such as were eager to seek after knowl

译：他为求学若渴的人打开了一扇门.这是as用作关系代词引导限制性定语从句的情况,一般与such联用,在从句中作主语,此时as 不可省略!定语从句一定得有先行词,而这句话里还一定要有关系代词,因为were eager……缺主语.such as这个搭配就有先行词＋关系代词的功用,相当于the people that.如果遇到such +n.as这种结构,例如：Such people as you describe are rare nowadays.已经有先行词people了,such就是当作定语.as还是关系代词,在这里当宾语.“你说的这种人现在很少啦!”