$$\frac{(304)^5}{(29.7)(399)^4} \approx \frac{300^5}{30\cdot400^4} = \frac{3^5 \cdot 10^{10}}{3\cdot 4^4 \cdot 10^9} = \frac{3^4\cdot 10}{4^4} = \frac{810}{256}$$
Which is closest to $3\rightarrow\boxed{\text{D}}$.
(The original expression is approximately equal to $3.44921198$.)