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题库 / Prep2008E2-SC-197
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.
a greater proportion than it was
a greater proportion than
a greater proportion than they have been
which is greater than was so
which is greater than it has been
请看讲解视频
c应该是they have done？
in any previous election是个明显的时间提示词，应该用过去完成时。但have been与前面的accounted for不平行，所以，感觉要用也只能用have done了
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