SC987的几道题

50.        According to some economists, the July decrease in unemployment so that it was the lowest in two years suggests that the gradual improvement in the job market is continuing. E

(A) so that it was the lowest in two years

(B) so that it was the lowest two-year rate

(C) to what would be the lowest in two years

(D) to a two-year low level（E）

(E) to the lowest level in two years

这两道题有点糊涂，为什么50不能选D，60不能选A呢？

哪位高手给指点一下吧~