A：$f\left(-\frac{3}{4}\right)>f\left(a^4+a^2+1\right)$

B：$f\left(-\frac{3}{4}\right)\ge f\left(a^4+a^2+1\right)$

C：$f\left(-\frac{3}{4}\right)<f\left(a^4+a^2+1\right)$

D：$f\left(-\frac{3}{4}\right)\le f\left(a^4+a^2+1\right)$