BPP Revision Kit question 13

Hi,

In BPP Revision kit question 13:

In material flow cost accounting (mfca), input manufacturing costs are categorised into material cost, waste tratment cost and which of the following?

According to answer sheet, the correct answer is D positive products cost and negative product costs.

Should it be A System cost and energy costs?

As it also stated in answer sheet:
Input cost: Material cost, waste management cost, energy cost, system cost.
Output cost: positive products cost and negative product costs.

I am a little confused.

Many thanks,
Lucy