Which of the following shows the correct relation? (nboiler denotes efficiency of a boiler)

• A. nboiler = (rate of energy absorption by water to form steam / rate of energy released by the combustion of fuel)
• B. nboiler = (rate of energy absorption by water to form steam + rate of energy released by the combustion of fuel)
• C. nboiler = (rate of energy absorption by water to form steam – rate of energy released by the combustion of fuel)
• D. nboiler = (rate of energy absorption by water to form steam x rate of energy released by the combustion of fuel)