ACME Corporation Used to Produce $50 Worth of Goods (In

ACME Corporation used to produce $50 worth of goods (in 2000 dollars) per million BTUs used. Now it produces $60 worth of goods (in 2000 dollars) per million BTUs. Based on this, we can conclude

A) nothing about ACME's energy efficiency.
B) that ACME's energy efficiency has declined.
C) that ACME's energy efficiency has improved.
D) that ACME is using a single energy source and achieving economies of scale in production.