The diagram depicts a low-voltage circuit used to heat the water in a fish tank. The heater has a resistance of $3.0\,\Omega$. The power supply has an e.m.f. of $12\,\text{V}$ and an internal resistance of $1.0\,\Omega$. At what rate is energy transferred to the heater?
- A$27\,\text{W}$
- B$36\,\text{W}$
- C$48\,\text{W}$
- D$64\,\text{W}$