C 比较的是 proportion和proportion,所以不应该用they.整个句子结构,a greater...这句应该是临近修饰more than half the spending的,可以补出来 which is a greater proportion. 又根据比较对称的原则,所以proportion应该跟proportion比较,我认为应该是
a greater proportion than the proportion had been ,如果要用代词,则可以表达成a greater proportion than it had been.