Final answer:
The effort force is applied perpendicular to the slope of an inclined plane, when it is applied to the lower edge (height) of the wedge.
Step-by-step explanation:
The effort force is applied perpendicular to the slope of an inclined plane, when the effort force is applied to the lower edge (height) of the wedge.
When an object rests on an incline, the force of gravity acting on the object is divided into two components: a force acting perpendicular to the plane (weight perpendicular to the slope) and a force acting parallel to the plane (weight parallel to the slope). In the case of an inclined plane, the effort force is applied perpendicular to the slope to counteract the weight perpendicular to the slope and prevent the object from sliding down.
Therefore, the correct answer is option c) perpendicular, lower.