Find $\frac{d^{2} y}{d x^{2}}$
\[
y=7 x^{4}-4 x^{2}+6
\]
A. $28 x^{2}-8$
B. $28 x^{2}-8 x$
C. $84 x^{2}-8$
D. $84 x^{2}-8 x$

Step 1 ：The problem is asking for the second derivative of the function \(y=7 x^{4}-4 x^{2}+6\). The second derivative is the derivative of the derivative. So, first, we need to find the first derivative of the function, then find the derivative of the result.

Step 2 ：First, let's find the first derivative of the function \(y=7 x^{4}-4 x^{2}+6\). Using the power rule for differentiation, which states that the derivative of \(x^{n}\) is \(n x^{n-1}\), we get \(y'=28 x^{3}-8 x\).

Step 3 ：Next, we find the second derivative by differentiating \(y'=28 x^{3}-8 x\). Again using the power rule, we get \(y''=84 x^{2}-8\).

Step 4 ：Final Answer: The second derivative of the function \(y=7 x^{4}-4 x^{2}+6\) is \(\boxed{84 x^{2}-8}\).