prep破解版2-28

28.   (25890-!-item-!-188;#058&002817)

In 1997, despite an economy that marked its sixth full year of uninterrupted expansion with the lowest jobless rate in a quarter century, the number of United States citizens declaring themselves bankrupt has jumped by almost 20 percent, at 1.34 million.

(A) declaring themselves bankrupt has jumped by almost 20 percent, at

(B) declaring themselves bankrupt jumped by almost 20 percent, to

(C) who declared themselves bankrupt has jumped by almost 20 percent, to

(D) who declared themselves bankrupt jumped almost by 20 percent, at

(E) to declare themselves bankrupt jumped almost by 20 percent, at

答案选b，为什么c不对呢？是has完成时不对，还是who前面应该加逗号？

请指点