Soaring television costs accounted for more than half the spending in the presidential campaign of 1992, a greater proportion than it was in any previous election.
Soaring television costs accounted for more than half the spending in the presidential campaign of 1992, a greater proportion than it was in any previous election.
(B) Correct;原句补完整:Soaring television costs accounted for more than half the spending in the presidential campaign of 1992, a greater proportion than(the proportion)(television costs had accounted for of the spending)in any previous election;这个句子中只是单个名词(proportion)的比较,所以不需要考虑than后面补出主谓,只补出介词短语就够了,不用担心后面的介词短语in any previou election没有平行对象
(C) 现在完成时使用错误,in any previous election说明应用过去完成时;they指代soaring television costs,使逻辑意义错误,比较结构需要比较对象对等,前者为a great proportion 是一个量词不能和具体的费用对比,而且其他的election不一定是soaring的;同时have been与前面的accounted for不平行,只要也要用have done。