The money spent on social insurance lastyear was four times ___ ten years

The money spent on social insurance lastyear was four times ___ ten years
A.that as much of B.as much as C.as much as D.as much as of that
这道题我做的答案是D,老师报的答案是C,理由是平行结构,前面为last year,后为ten years ago,不用of.
但我在网上一查也看到有说选D,到底选哪个比较好呢?