The electromagnetic field transforms as a tensor:
$\begin{align*}F^{\mu' \nu'} = \Lambda_{\lambda}^{\mu'} \Lambda_{\sigma}^{\nu'} F^{\mu \nu}\end{align*}$
where $F^{\mu \nu}$ is the field tensor
$\begin{align*}F^{\mu \nu} = \left(\begin{array}{cccc}0 & E_x/c & E_y/c & E_z/c \\- E_x/c & 0 & B_z & ...$
and $\Lambda_{\lambda}^{\mu'}$ and $\Lambda_{\sigma}^{\nu'}$ are Lorentz transformation matrices:
$\begin{align*}\Lambda_{\lambda}^{\mu'} = \Lambda_{\sigma}^{\nu'} = \left(\begin{array}{cccc}\gamma & - \gamma \beta &...$
for the standard case when the velocity of the primed frame with respect to the unprimed frame is in only the $x$ direction. Therefore, answer (B) is correct.

Solution to 1986 Problem 22