In order to determine if the given lines are perpendicular, parallel or neither parallel nor perpendicular, you take into account that parallel lines are those that never cross between them in space.
Perpendicular lines are those which form an angle of 90° when they croos to each other.
With previous clarifications you can conclude that:
EF and CD are perpendicular between them.
GH and EF are not perpendicular and parallel between them.
AB and CD are parallel between them
