4. (8 points) As shown in the figure, a conical container is filled with 50 liters of water, and the water level is half the height of the cone. This container is half full. The maximum amount of water this container can hold is ( ) liters.
A. 100
B. 200
C. 400
D. 800
【Solution】Solution: According to the analysis, it is easy to know that the height of the container is twice the height of the water surface, that is: $H=2 h, R=2 r$, as shown in the figure:

According to the volume formula of a cone: $V=\frac{1}{3} \pi r^{2} h$. We get:
$$
V_{\text {large }}=\frac{1}{3} \pi R^{2} H=\frac{1}{3} \pi(2 r)^{2} \times(2 h)=8 \times \frac{1}{3} \pi r^{2} h=8 V_{\text {water }}=8 \times 50=400 L
$$

Therefore, the correct choice is: $C$.