Question ID:PT72 S2 Q2 Passage:Archaeologist: For 2,000 years the ancient Sumerians depended on irrigation to sustain the agriculture that fed their civilization. But eventually irrigation built up in the soil toxic levels of the salts and other impurities left behind when water evaporates. When its soil became unable to support agriculture, Sumerian civilization collapsed. A similar fate is thus likely to befall modern civilizations that continue to rely heavily on irrigation for agriculture.  Stem:Which one of the following, if true, most weakens the archaeologist's argument? Correct Answer Choice:CChoice A:Most modern civilizations could not feed themselves through agriculture without relying heavily on irrigation. Choice B:Factors unrelated to the use of irrigation would probably have caused Sumerian civilization to collapse sooner or later. Choice C:Many modern farmers use irrigation techniques that avoid the buildup of salts and other toxic impurities in the soil. Choice D:Many modern civilizations do not rely to any significant extent on irrigation for agriculture. Choice E:The soil of ancient Sumeria already contained some toxic salts and other impurities before the Sumerians started using irrigation for agriculture.