A Nuclear Submarine Uses Its Reactor to Heat Water/steam to a Temperature

A nuclear submarine uses its reactor to heat water/steam to a temperature of 950 ^$\circ$ C.The steam drives turbines that turn the submarines propellers.After the steam passes through the turbines it is cooled to 4 ^$\circ$ C and condensed by the seawater that surrounds the submarine and returned to be heated by the reactor again.What is the upper limit of the efficiency of the submarine's turbines?

A) 21.7%
B) 38.6%
C) 77.4%
D) 85.1%
E) 99.6%