What is meant by a 15-30-15 fertilizer?

• A. 15 parts Nitrogen, 30 parts Potassium, 15 parts Phosphorous
• B. 15 parts Nitrogen, 30 parts Phosphorous, 15 parts Potassium
• C. 15 parts Nitrogen, 30 parts Magnesium Sulfate, 15 parts Potassium
• D. 15 parts Nitrogen, 30 parts Manganese, 15 parts Potassium