sat OG语法一题In Germany,foresters discovered that trees killed

sat OG语法一题
In Germany,foresters discovered that trees killed by acid rain had begun to die four years earlier,even though the trees had shown no signs of disease then.
A
B earlier,but not showing any signs of disease then
C earlier,no outward signs of disease had been shown then in the trees,however
D earlier without any signs of disease shown then
E earlier,not then having shown any signs of disease,however
为啥选A不选D啊

答案的确是A.even though表示转折意思“尽管”,逻辑上正确；再者,时态用的是had shown也没问题.
D不正确,虽然without这个结构用的很好,但是without是介词,后面要跟上名词或动名词(V-ing),但D选项后面用的是shown过去分词,不对.至少要改成without any signs of disease being shown then才语法正确,但这样又不符合SAT的简洁性原则,所以不能选.