The NPK Percentages on a Package of Fertilizer Refer to the

The NPK percentages on a package of fertilizer refer to the

A) total protein content of the three major ingredients of the fertilizer.
B) percentages of manure collected from different types of animals.
C) relative percentages of organic and inorganic nutrients in the fertilizer.
D) percentages of three important mineral nutrients.
E) proportions of three different nitrogen sources.