A Carnot engine, whose efficiency is $$40\%$$, takes in heat from a source maintained at a temperature of $$500\ K$$. It is desired to have an engine of efficiency $$60\%$$. Then, the intake temperature for the same exhaust (sink) temperature must be

A

efficiency of Carnot engine cannot be made larger than $$50\%$$

B

$$1200\ K$$

C

$$750\ K$$

D

$$600\ K$$