c. \( k^{3} k^{5}-4\left(k^{4}\right)^{2} \)

Let's first simplify the expression \( k^{3} k^{5}-4\left(k^{4}\right)^{2} \): By using the properties of exponents, we can combine the first term: \[ k^{3} k^{5} = k^{3+5} = k^{8} \] Now, let's simplify the second term: \[ \left(k^{4}\right)^{2} = k^{4 \times 2} = k^{8} \] So, we have: \[ -4\left(k^{4}\right)^{2} = -4k^{8} \] Putting these together, we get: \[ k^{8} - 4k^{8} = (1 - 4)k^{8} = -3k^{8} \] Thus, the simplified expression is: \[ -3k^{8} \]