ANSWER
Option B and C are equivalent.
EXPLANATION
[tex](\frac{1}{4})^{3x^2}[/tex]
Recall that,
[tex]\frac{1}{a^m}=a^{-m}[/tex]
This implies that,
[tex](\frac{1}{4})^{3x^2}=(4^{-1})^{3x^2}[/tex]
Recall again that,
[tex](a^m)^n=a^{mn}[/tex]
This implies that,
[tex](\frac{1}{4})^{3x^2}=(4)^{-3x^2}[/tex]
So we simplify option C to obtain option B. Hence the two are equivalent.
