On His Honeymoon, James Joule Attempted to Explore the Relationships $4186 \mathrm {~J} / \mathrm { kg } \cdot \mathrm { K }$

On his honeymoon, James Joule attempted to explore the relationships between various forms of energy by measuring the rise of temperature of water which had fallen down a waterfall on Mount Blanc. What maximum temperature rise would one expect for a waterfall with a vertical drop of 20 m? The specific heat of water is $4186 \mathrm {~J} / \mathrm { kg } \cdot \mathrm { K }$

A) $0.064 \mathrm { C } ^ { \circ }$
B) $0.047 \mathrm { C } ^ { \circ }$
C) $0.071 \mathrm { C } ^ { \circ }$
D) $0.053 \mathrm { C } ^ { \circ }$