An electromagnetic wave in vacuum has the electric and magnetic fields $\overrightarrow{\mathrm{E}} \mathrm{and} \overrightarrow{\mathrm{B}}$, which are always perpendicular to each other. The direction of polarization is given by $\overrightarrow{\mathrm{X}}$ and that of wave propagation by $\overrightarrow{\mathrm{k}}$. Then :

• A

  $\overrightarrow{\mathrm{X}}\parallel \overrightarrow{\mathrm{E}} \mathrm{and} \overrightarrow{\mathrm{k}}\parallel \overrightarrow{\mathrm{E}} \mathrm{x} \overrightarrow{\mathrm{B}}$

• B

  $\overrightarrow{\mathrm{X}}\parallel \overrightarrow{\mathrm{B}} \mathrm{and} \overrightarrow{\mathrm{k}}\parallel \overrightarrow{\mathrm{E}} \mathrm{x} \overrightarrow{\mathrm{B}}$

• C

  $\overrightarrow{\mathrm{X}}\parallel \overrightarrow{\mathrm{E}} \mathrm{and} \overrightarrow{\mathrm{k}}\parallel \overrightarrow{\mathrm{B}} \mathrm{x} \overrightarrow{\mathrm{E}}$

• D

  $\overrightarrow{\mathrm{X}}\parallel \overrightarrow{\mathrm{B}} \mathrm{and} \overrightarrow{\mathrm{k}}\parallel \overrightarrow{\mathrm{B}} \mathrm{x} \overrightarrow{\mathrm{E}}$