一道SAT语法题In Germany,foresters discovered that trees killed by

一道SAT语法题
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)
B.ealier,but not showing any signs of disease then
C.ealier without any signs of disease shown then
请问为什么第一个是最好的

这道题其实不用考虑的太多,楼主注意时态就ok了 因为这句话大概意思就是,在德国,科学家发现四年前被酸雨淋过的树木都死了,尽管在那时那些树木并没有显示任何的征兆.所以,这道题不用考虑太多,树木显示征兆 一定是发生在树木死亡之前的.所以从时态来讲,第一项选择是对的.
希望能够帮到楼主
晓篱 敬上