To simplify the expression $(b^5)^4$, you apply the power of a power rule in exponents, which states:

$(a^m)^n = a^{m \cdot n}$

Here, $b^5$ is raised to the power of 4, so:

$(b^5)^4 = b^{5 \cdot 4} = b^{20}$

Thus, the correct simplification is:

$\boxed{b^{20}}$

Would you like further details or have any questions?

5 Related Questions:

1. How do you simplify $(x^3)^6$?
2. What is the result of $(a^7)^2$?
3. How do you simplify $(y^2)^5 \cdot (y^3)^2$?
4. What is the rule for dividing powers with the same base, like $\frac{a^6}{a^3}$?
5. How would you simplify $(b^2)^3 \cdot (b^4)^2$?

Tip:

When dealing with powers raised to another power, always multiply the exponents to simplify.