An electromagnetic wave travelling along z-axis is given as: E= Eo cos(kz - ωt). Choose the correct options from the following;
(a) The associated magnetic field is given as B=1/c k x E=1/ω(k X E).
(b) The electromagnetic field can be written in terms of the associated magnetic field as E=c(B x k).
c) k.E = 0, k.B=0.
(d) k ×E = 0,k × B=0.