4. The ratio of land area to ocean area on Earth's surface is $29: 71$, and three-quarters of the land is in the Northern Hemisphere. Therefore, the ratio of ocean area in the Southern Hemisphere to that in the Northern Hemisphere is ( )
A. $284: 29$
B. $284: 87$
C. $87: 29$
D. $171: 113$
4. Solution: Let the surface area of the Earth be 1,

then the ocean area of the Northern Hemisphere is: $0.5-0.29 \times \frac{3}{4}=\frac{2-0.87}{4}=\frac{1.13}{4}$
the ocean area of the Southern Hemisphere is: $0.71-\frac{1.13}{4}=\frac{2.84-1.13}{4}=\frac{1.71}{4}$
the ratio of the ocean area between the Northern and Southern Hemispheres is: $\frac{1.71}{4}: \frac{1.13}{4}=171: 113$
Answer: D