In a Counter flow heat exchanger design, fluid rates and specific heats were chosen in such a manner that heat capacities of both the fluids are same. A hot fluid enters at $$100^\circ$$ C and leaves at $$60^\circ$$C. The cold fluid enters heat exchanger at $$40^\circ C$$. The mean temperature difference between the two fluids is

A

$$40^\circ C$$

B

$$60^\circ C$$

C

$$20^\circ C$$

D

$$36.6^\circ C$$