Spokesperson: Contrary to what some have claimed, our group’s “Clean ... ...

Spokesperson: Contrary to what some have claimed, our group’s “Clean City” campaign has been a rousing success. After all, the amount of trash on the city’s streets today is significantly lower than when the campaign began. Which one of the following is an assumption required by the spokesperson’s argument?
(A) The amount of trash on the city’s streets was not declining at the same rate or faster before the campaign began than it did during the campaign.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Oct 2012 LSAT (PT67): Logical Reasoning B