大全138 过去时态问题

138. As sales of cars and light trucks made in North America were declining 13.6 percent in late February, many analysts conclude that evidence of a recovering automotive market remains slight.
(A) As sales of cars and light trucks made in North America were declining 13.6 percent in late February, many analysts conclude
(B) Since sales of cars and light trucks made in North America declined 13.6 percent in late February, and many analysts conclude
(C) With sales of cars and light trucks made in North America declining 13.6 percent in late February, with many analysts concluding
(D) Because sales of cars and light trucks made in North America declined 13.6 percent in late February, many analysts concluded
(E) Because of sales of cars and light trucks made in North America declining 13.6 percent in late February, therefore, many analysts concluded

答案是D
中两个动作的时态来看好象都是指都在in late February发生的,可是我觉得conclude和decline有个先后关系吧?

in late February为什么只能用一般过去时呢,过去进行时不是也算过去范畴的时态?in late February下可以用么?