To find the area of the land required for planting 20,000 seeds at a density of 4,000 seeds per acre, you can use the formula:
\[ \text{Area (in acres)} = \frac{\text{Total number of seeds}}{\text{Planting density (seeds per acre)}} \]
Substituting the values:
\[ \text{Area} = \frac{20,000 \text{ seeds}}{4,000 \text{ seeds per acre}} = 5 \text{ acres} \]
So the correct answer is 5 acres.