Select the options that best complete the statement. positively charged particle trajectories(always, never, the same as)follow electric field lines, because(electric field lines are defined by the path positive test charges travel.,the particle velocities may or may not be in the same direction as the electric field lines.,positive charges repel each other and, therefore, are repelled by electric field lines.,the electric force on a positively charged particle is in the same direction as the electric field.)

a) always. b) electric field lines are defined by the path positive test charges travel.

Explanation:

By convention, field lines always follow the direction that it would take a positive test charge  (small enough so it can´t disrupt the field created by a charge distribution), under the influence of an electric field, at the same point where the test charge is located.

So any positive charge, subject to an electric field influence, moves along the field line that passes through its current position, in the same way that a positive test charge would.

We could say also that the electric force on a positively charged particle is in the same direction as the electric field that produces that force (due to some charge distribution) , which is true, but it doesn´t explain why.

i think the answer would be b