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. Which one of the following is an assumption on which the argument depends?
A: As far as soil health is concerned, aiding the decomposition of dead plants is the most important function performed by earthworms.
B: By itself, acidity of soil does nothing to hasten decomposition of dead plants.
C: Crushed limestone contains available calcium and magnesium, both of which are just as vital as earthworms to healthy soil.
D: 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.
Choose A, B, C or D as your solution.
D