The problem asks which expression is equivalent to $(8^5)^4$.

To solve this, we use the power of a power rule, which states: $(a^m)^n = a^{m \cdot n}$

In this case, $a = 8$, $m = 5$, and $n = 4$. So: $(8^5)^4 = 8^{5 \cdot 4} = 8^{20}$

Thus, the correct expression is $8^{20}$.

Would you like more details or have any further questions?

Here are 5 related questions you might find helpful:

1. How do you simplify $(x^3)^5$?
2. What is the difference between multiplying exponents and raising a power to a power?
3. How would you solve $(3^4)^2$?
4. Can the power of a power rule be applied to negative exponents?
5. How would you express $(2^2)^n$ in simplified form?

Tip: Always remember that when raising a power to another power, you multiply the exponents!