Fill in the blanks with appropriate words given in the answer choices.
Each of the sentences below has a blank space indicating that something has been omitted. Fill in the blank with the word that best fits the meaning of the sentence as a whole.
Any increase in coal-fired furnaces beyond a particular level necessitates greater recourse to fossil fuels; thus, the capability of an economy to effectively manage energy resources depends partially on………. the number of fired furnaces.