Organic fertilizers are made from mineral deposits along with bone meal, plant meal, or composted manure, while synthetic fertilizers are made by processing synthetic chemicals. The numeric ratio listed on a fertilizer, whether it's organic or synthetic, indicates the proportions of the primary nutrients—nitrogen, phosphate, and potash—inside. For example, a bag of fertilizer labeled 4-8-6 contains 4 percent nitrogen, 8 percent phosphate, and 6 percent potash. A 100-pound bag of 4-8-6 organic fertilizer and a 100-pound bag of 4-8-6 synthetic fertilizer may differ in other respects, but farmers can rest assured that the bags differ neither in the amount of primary nutrients they deliver into soil, nor in the time period those nutrients remain available to plants' root systems.
Which of the following, if true, most strengthens the argument above?
【选项】
A variety of different tests found that levels of contaminants in distinct soils that had been treated with a volume of 4-8-6 synthetic fertilizer were no higher than those in samples treated with a volume of 4-8-6 organic fertilizer.
选项是否正确？