$$100 \, \text{g}$$ of water is heated from $$30^\circ \text{C}$$ to $$50^\circ \text{C}$$. Ignoring the slight expansion of the water, the change in its internal energy is (specific heat of water is $$4148 \, \text{J/kg/K}$$):

A

$$8.4 \, \text{kJ}$$

B

$$84 \, \text{kJ}$$

C

$$2.1 \, \text{kJ}$$

D

$$4.2 \, \text{kJ}$$