Material Flow Cost Accounting

Hi John, I have a doubt regarding this topic. Here’s the question from the BPP Revision Kit:

In material flow cost accounting, input manufacturing costs are categorized into material costs, waste treatment costs and which of the following?

A) System costs and energy costs
B) Positive product costs
C) Negative product costs
D) Positive product costs and negative product costs

I answered A but the answer is actually D. Would you mind explaining to me?