两道困惑题，求解答

maggiehhm

The period when the great painted caves atL and A were occupied by UP peoples has been established by carbon dating, butwhat is more difficult to determine is the use to which primitive peoples put the caves, the reasonsfor their decoration, and the meaning of the magnificently depicted animals.
如标注，为什么用的是is不是are？
Soaring television costs accounted for morethan half the spending in the presidential campaign of 1992. a greaterproportion than it was inany previous election.
than后面的it was究竟要不要加上，为什么
就要考试了，麻烦NN们解答下~

bitieming

第一个。but后面句子的主语是what引导的主语从句，主语从句都是单数
第二个。要去掉啊，这个比较属于局部比较中的介词结构比较，就是比较内容与主句内容一致。补完后面那个比较就可以看出来，补完壶是 a great porpotion than soring tv costs accounted for in any...，补出内容因为跟前面一致所以省略~