请教一道语法题

xd2008

After gradual declension down to about 39 hours in 1970, the workweek in the United States has steadily increased to the point that the average worker now puts in an estimated 164 extra hours of paid labor a year.

(A)   After gradual declension down

(B)   Following a gradual declension down

(C)   After gradual declining down

(D)  After gradually declining

(E)   Following gradually declining

答案是D，E呢？after和following怎么区别？

serendipityh

following 是分词
说明它的动作的执行者是the workweek, workweek 跟随这正在下降, 相当没有逻辑
the workweek 的动作应该是下降
我刚看这时被diclension 给迷惑了, 我以为它有特殊意思, 晕菜! 原来还是下降.