Correct option is A. $$3.6\times 10^6$$
$$1$$ kilowatt-hour(kWh) is a unit of energy. Normally, we want energy to be expressed in joules(J) and time in seconds(s).
Energy(kWh)$$=$$Power(kW)$$\times$$(h)$$=1000$$W$$\times 3600$$s$$=1000$$J/s$$\times 3600$$s$$=3600000$$J$$=3.6\times 10^6$$J.