大全50,请教

fair_sword

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.
(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) to the lowest level in two years
正确答案E,
问题：the decrease to the lowest level in two years是个什么结构，C,D错在那里，谢谢！

dreadpower

选项C：what would be 多余（SC中的一个系统错误,what从句多余）
选项D：to a two-year low level （降）到一个两年的低水平，没体现原句lowest的意思
           意思上也有问题，一个是两年的低水平，一个是在两年内降到最低水平