If a : b = b : c, then a4 : b4 would be equal to

Answer: Option B

$$\begin{array}{rl}& =\frac{a}{b}=\frac{b}{c}\\ & \Rightarrow b^2=ac\\ & \Rightarrow \frac{a^4}{b^4}=\frac{a^4}{{\left(ac\right)}^2}\\ & =\frac{a^4}{a^2{c}^2}\\ & =\frac{a^2}{c^2}\\ & \Rightarrow a^4:b^4=a^2:c^2\end{array}$$