....the amount of contribution (that) they do(contribute)
... the amount of earning (that) they do(earn)
... the amount of driving (that) they do(drive)
原来如此..谢谢…但这样有什么意义??省略的that是指代the amount of driving吗??原句就变few people drive the amount of driving??不懂为什么要这样写??若后面没有they do也可以很清楚表达the amount of driving跟few people有关啊..还是可以改写为the amount of their driving??