Evaluate $\underset{x}{lim}f(x)$ and $\underset{x-}{lim}f(x)$ for the rational function. Then give the horizontal asymptote of $f(f,$any$)$

$f(x)=\frac{21x^5-7}{3x^5-2x^4}$

Select the correct choice below, and, if necessary, fill in the answer box to complete your choice

A$.\underset{x-}{lim}\frac{21x^5-7}{3x^5-2x^4}=7($Simplify your answer$)$

B$.$ The limit does not exist and is neither $$ or $-$

Seted the correct chitce betow, and, If necessary, fill in the answer box to complete your choice

A$.\underset{x}{lim}\frac{21x^5-7}{3x^5-2x^4}=7($Simplify your answer$)$

R$.$ The limit does not exist and is neither $$ of $-.$

Select the correct choice below, and if necessary, fill in the answer box to complete your choice.

A$.$ The function has a horizontal asymptote at $y=$

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