$A$ plane electromagnetic wave of wavelength $\lambda$ has an intensity $I$. It is propagating along the positive $Y$-direction. The allowed expressions for the electric and magnetic fields are given by:

• A
  $\vec E = \sqrt{\frac{I}{\varepsilon_0 c}} \cos \left[ \frac{2\pi}{\lambda}(y - ct) \right] \hat i; \vec B = \frac{1}{c} E \hat k$
• B
  $\vec E = \sqrt{\frac{I}{\varepsilon_0 c}} \cos \left[ \frac{2\pi}{\lambda}(y - ct) \right] \hat k; \vec B = -\frac{1}{c} E \hat i$
• C
  $\vec E = \sqrt{\frac{2I}{\varepsilon_0 c}} \cos \left[ \frac{2\pi}{\lambda}(y - ct) \right] \hat k; \vec B = +\frac{1}{c} E \hat i$
• D
  $\vec E = \sqrt{\frac{2I}{\varepsilon_0 c}} \cos \left[ \frac{2\pi}{\lambda}(y + ct) \right] \hat k; \vec B = \frac{1}{c} E \hat i$