PT 66 S2 Q24

Had the party’s economic theories been sound and hadit succeeded in ... ...

The flawed reasoning in which one of the following arguments most closely resembles the flawed reasoning in the argument above?
(A) If the people who inhabited the valley for so long had been invaded, or if there had been a dramatic climatic change, there would have been changes in the valley’s architecture. But architecture in the valley remained the same throughout their stay. Thus, the valley people must not have been invaded at any time during their stay.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in June 2012 LSAT (PT66): Logical Reasoning A