base是及物动词, 以…作基础,所以常见的还有被动式be based on...his novel is based on a true story
选d...which指代ground...前面的介词on必须有,因为这里相当于用了baseontheground这个短语..在定语从句中当用which指代了ground,ground前面的on还是应该存在.但这时候自然要加在which前面,所以变成了onwhichtobase