when b>0 and d is a positive integer, (b)-2/d is equivalent to which of the following expression

the given exoression is
[tex]=b^{-\frac{2}{d}}[/tex]so,
[tex]b^{-\frac{b}{2}}=\frac{1}{b^{\frac{2}{d}}}[/tex][tex]=\frac{1}{(\sqrt[d]{b})^2}[/tex]thus, the correct answer is option A