Direction of the Acceleration of a Proton

A proton is moving in an electric field. The direction of the acceleration of the proton is

a) in the direction the proton is moving.
b) opposite the direction the proton is moving.
c) perpendicular to the direction the proton is moving.
d) in the direction of the electric field.
e) opposite the direction of the electric field.

D. The electric field is defined as the force on a positive charge.
A proton is a positive charge so the electric field provides a force and an acceleration in that direction.

(d). F = +qE which is a vector equation & so equates direction as well as magnitude.