Answer:
[tex]\textbf{A. }\quad\dfrac{b^4}{a}[/tex]
Step-by-step explanation:
The applicable rules of exponents are ...
(a^b)/(a^c) = a^(b-c)
a^-b = 1/a^b
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The expression can be rewritten as ...
[tex]\dfrac{a^3b^5}{a^4b}=a^{3-4}b^{5-1}=a^{-1}b^4\\\\=\boxed{\dfrac{b^4}{a}}[/tex]
