d
\(\because \overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{B}} \| \overrightarrow{\mathrm{v}}\)

Given that wave is propagating along positive \(z\) -axis and \(\overrightarrow{\mathrm{E}}\) along positive \(x\) -axis. Hence \(\overrightarrow{\mathrm{B}}\) along \(\mathrm{y}\) -axis. 

From Maxwell equation 

\(\overrightarrow{\mathrm{V}} \times \overrightarrow{\mathrm{E}}=-\frac{\partial \mathrm{B}}{\partial \mathrm{t}}\)

i.e. \(\frac{\partial E}{\partial Z}=-\frac{\partial B}{d t}\) and \(B_{0}=\frac{E_{0}}{C}\)