Question ID:PT53 S1 Q15 Passage:Earthworms, vital to the health of soil, prefer soil that is approximately neutral on the acid-to-alkaline scale. Since decomposition of dead plants makes the top layer of soil highly acidic, application of crushed limestone, which is highly alkaline, to the soil's surface should make the soil more attractive to earthworms.  Stem:Which one of the following is an assumption on which the argument depends? Correct Answer Choice:BChoice A:As far as soil health is concerned, aiding the decomposition of dead plants is the most important function performed by earthworms. Choice B:After its application to the soil's surface, crushed limestone stays in the soil's top layer long enough to neutralize some of the top layer's acidity. Choice C:Crushed limestone contains available calcium and magnesium, both of which are just as vital as earthworms to healthy soil.  Choice D:By itself, acidity of soil does nothing to hasten decomposition of dead plants. Choice E:Alkaline soil is significantly more likely to benefit from an increased earthworm population than is highly acidic soil.