The trajectory of charged particles in an electric field a. must be along the electric field line always. b. must be tangential to the electric field line. c. is always circular. d. must be perpendicular to the electric field line. e. is always elliptical. f. is not the same as a field line, in general.

a. must be along the electric field line always.

Explanation:

A charged particle in a region where there is an electric field, experiences a force equal to the product of its charge by the intensity of the electric field. If the charge is positive, the force exerted by the electric field is in the direction of the field lines. If the charge is negative, the force exerted by the electric field is in the opposite direction to the direction of the field lines.