Bài giải:

f(x) = $8-{{x}^{5}}+4x-2{{x}^{3}}+{{x}^{2}}-7{{x}^{4}}$

f(x) = $-{{x}^{5}}-7{{x}^{4}}-2{{x}^{3}}+{{x}^{2}}+4x+8$

g(x) = ${{x}^{5}}-8+3{{x}^{2}}+7{{x}^{4}}+2{{x}^{3}}-3x$

g(x) = ${{x}^{5}}+7{{x}^{4}}+2{{x}^{3}}+3{{x}^{2}}-3x-8$

h(x) = f(x) + g(x) = ($-{{x}^{5}}-7{{x}^{4}}-2{{x}^{3}}+{{x}^{2}}+4x+8$) + (${{x}^{5}}+7{{x}^{4}}+2{{x}^{3}}+3{{x}^{2}}-3x-8$)

h(x) = $(-{{x}^{5}}+{{x}^{5}})+(-7{{x}^{4}}+7{{x}^{4}})+(-2{{x}^{3}}+2{{x}^{3}})+({{x}^{2}}+3{{x}^{2}})+(4x-3x)+(8-8)$

h(x) = $4{{x}^{2}}+x$

h(x) = 0 $\Leftrightarrow $ $4{{x}^{2}}+x=0$

$\Leftrightarrow $x(4x + 1) = 0

$\Leftrightarrow \left[ \begin{align}  & x=0 \\  & 4x+1=0 \\ \end{align} \right.$

$\Leftrightarrow \left[ \begin{align} & x=0 \\ & x=-\frac{1}{4} \\ \end{align} \right.$

Vậy đáp án đúng là: C